Add optional signup

Fix default settings when they are boolean.

error is that ```enabled ||= true``` always evaluates to true.
Change all initialization of bool settings to use the same syntax:
```setting = true if setting.nil?```

Improve setup task, by making it less dangerous

Eliminate horizontal shifting on diff body heights

switch to use link_to_member to prevent 500 if user is a project owner but does not have membership and leave comment

Add SSH custom port support for install/installation.md

Allow the OmniAuth provider args parameter to be passed through

Fixes #2608

Merge branch 'check_gitlab_in_git_group' of https://github.com/VonC/gitlabhq into VonC-check_gitlab_in_git_group

Fixes #2166

Fixes #2617