Creates common directives file

Instead of having separate directive files. Specific directive files
will go within their correponding section folder (e.g. dashboard)
Adds links to preview page in the item list widget
CRAFTERCMS-316: Click pencil icon to see edit panel at bottom of page
Merge remote-tracking branch 'david/master'
Adds a generator to create the json for the dashboard widgets
CRAFTERCMS-311: Additonal Widgets for Dashboard

Adds additional widgets to the dashboard: Recently Made Live,
Approved Scheduled Items & Go Live Queue
Lints code
Adds visual cue to sort order in dashboard widgets
Merge remote-tracking branch 'david/master'
Adds testing site and updates install instructions
Merge remote-tracking branch 'david/master'
Mock Implementation
Initial Mock Implementation of studio-api.