Also, remove ephemeral messages after 10 seconds, not 20

Use-case is when an invalid MUC gets opened in singleton mode.
Without this fix a new chat with spinner appears, even though it
shouldn't.

updates #555

- Remove the `keepalive` configuration setting. It is now always implicitly `true`.
- Remove the `expose_rid_and_sid` configuration setting.
- A `prebind_url` is now mandatory when setting `authentication` to `prebind`.
- It's no longer possible to pass in `rid` and `sid` values to `converse.initialize.

I'm using prettierx, which is a fork of prettier so that we can have
spaces before the brackets in a function declaration.

I don't like how restrictive prettier is concerning its configuration
and formatting.

- it messes up some indentation in specs/
- it removes a second newline when I specifically want to have two
- it doesn't allow spaces before brackets in function declarations (hence prettierx)
- it adds spaces for function parameters with default values

None of this is configurable.

So auto-formatting is not turned on by default, but it might be a useful
tool in some cases.

Fixes an issue where indentation was off in converse-core.js, causing
vim-sleuth to wrongly indent by three spaces only.

- fix import path
- remove unnecessary lines in webpack config
- remove unused file

updates #1111

* Checkmark and edit modal button are now on the right
* Instead of showing checkmarks for MUC messages,
  we now show them as light grey before MUC reflection
* Simplify message markup by requiring less `if` statements

Also, set the resource in `setUserJID`

- New plugin `converse-smacks`
- New config option `enable_smacks`
- Rename session cache id from `converse.bosh-session` to `converse.session`
- Refactor logout and login as consistently used api methods
- Refactor session cache to store per JID

Fixes #316

So that we can specify defaults

When a synchronous event is fired, Converse will wait for all
promises returned by the event's handlers to finish before continuing.

if the page is reloaded while the nickname form is shown

We now use CSS to make sure that the controlbox and toggle is always on the far right.