Add "Requires Input" JS behavior

This aims to replace all of those `disableButtonIfEmptyField` calls littered throughout views and JS with a simple, clean, markup-based behavior.

While going through all of the old usages, I found a few places where the old behavior wasn't actually working, so... bonus, they work now!

See merge request !900

Remove jasmine:ci task, execute teaspoon directly on CI

See merge request !901

The "Begin with the selected commit" checkbox requires the submit button
to be enabled, even if the extended SHA1 input field is blank.

These have been replaced by the "requiresInput" behavior.

Rename abilities to correspond contoller/model action names

write_ was renamed to create_
modify_  was renamed to update_

So now in update action we have next code

```
def create
  can?(current_user, :create_issue, @issue)
end

def update
  can?(current_user, :update_issue, @issue)
end
```

See merge request !896

Reorder MergeRequestTabs constructor

The tab was being activated before we set the `[commits|diffs]Loaded`
variable, so even when the `/diffs` route is accessed directly, like
from the "Side-by-side" link, the tab was being loaded from its default
source.

Fixes #1887

See merge request !892

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Update permissions for issue tracker management

Don't allow guest or reporter to set assignee, milestone and label when create or update new issue and merge request.
After this change `Guest` and `Reporter` rule is used to report issues but only `Developer` and higher roles can manage issues (schedule milestone, assign to user or close any issue)

Also I removed some duplication code between issues and merge requests and put all issuable partials in one directory

See merge request !890

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

write_ was renamed to create_
modify_  was renamed to update_

So now in update action we have next code

def create
  can?(current_user, :create_issue, @issue)
end

def update
  can?(current_user, :update_issue, @issue)
end
Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

added info about GitHub importing

Added info that importing doc also works for GitHub EE.

https://dev.gitlab.org/gitlab/gitlabhq/issues/2410#note_49396

See merge request !1878

Add SAML to list of social_provider

Resolves issue 1888.  Still an issue because the SAML link under Connected Accounts will not have a logo.

See merge request !891

The tab was being activated before we set the `[commits|diffs]Loaded`
variable, so even when the `/diffs` route is accessed directly, like
from the "Side-by-side" link, the tab was being loaded from its default
source.

Fixes #1887

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Have sidebar labels disappear behind content instead of hide immediately when collapsing.

I'm not sure how to make a gif out of it, but I promise it looks pretty :)

See merge request !888

prettier highlighting of active link in the sidebar

Before:

![Screenshot_2015-06-25_11.17.08](https://dev.gitlab.org/gitlab/gitlabhq/uploads/851606a122c1d1174d0f97857ad472d3/Screenshot_2015-06-25_11.17.08.png)

After:

![Screenshot_2015-06-25_11.17.42](https://dev.gitlab.org/gitlab/gitlabhq/uploads/b8dc55bcd76dac29652ef5d25f99ccff/Screenshot_2015-06-25_11.17.42.png)

Only with this theme it's not an improvement (this is an honest merge request (trademark pending)) :

![Screenshot_2015-06-25_11.18.35](https://dev.gitlab.org/gitlab/gitlabhq/uploads/5d631a11ee866f5fc51e985b02a836ba/Screenshot_2015-06-25_11.18.35.png)

See merge request !1879