Refactor the Issue Tracker forms in App
Simplify AppsController

 * avoid a filter to parse IssueTracker params
 * Add acceptance test with phantomjs to be sure the Apps editing works
   fine with IssueTracker
 * Add IssueTrackers::None the IssueTracker configure doing nothing
Add information in developper test about skipping js test
Extract all IssueTracker system and migrate to errbit_plugin

This new system can avoid having all dependencies in Errbit directly.
Now if you want new issue tracker you need add it. Not delete it like
previous.

This work is in progress actually
Update Gemfile with errbit_plugin and errbit_github_plugin
Update errbit_plugin to have all assets and all test pass
Use the old type in issue_tracker instead a fix one

Thanks @stevecrozz to report this error
Merge remote-tracking branch 'errbit/master' into features/extract_issue_tracker-merge_master

Conflicts:
	Gemfile
	Gemfile.lock
	app/models/issue_trackers/github_issues_tracker.rb
	app/models/issue_trackers/redmine_tracker.rb
	spec/models/issue_trackers/redmine_tracker_spec.rb
delegate tracker url

The apps index calls Tracker#url which doesn't exist. It should be
delegated to the underlying tracker instance.
https://github.com/errbit/errbit/blob/features/extract_issue_tracker/app/views/apps/index.html.haml#L40
have only one 'create issue' button

Formerly, if an app had a github repo, but another issue tracker was
configured, there would be two 'create issue' buttons (one for github
and one for the other issue tracker.) If there is an issue tracker
configured, we should use only that one.
Add spec for #655

Hint: This diff is much easier to read if you ignore whitespace
Update README.md
Joined all the attribute readers.
Moved long assignment into smaller more readable lines.
Cleaned the long unreadable statement into smaller seperate lines.
Removed extra empty line at the body end.
Changed to Ruby 1.9+ hash syntax.
Avoid double negation.
Merge pull request #652 from brandedcrate/features/extract_issue_tracker-merge_master

Features/extract issue tracker merge master
Merge pull request #653 from brandedcrate/features/extract_issue_tracker-delegate_url

delegate tracker url