Implemented Group API methods

- POST /v1/users
- DELETE /v1/users/:username/subscriptions/:userId
- PATCH /v1/users/:userId
- DELETE /v1/users/:userId
Added changes to work with Groups and added UI items for Groups
Added feed-factory
Implements adding and removing administrators. Fixes header-error
Adds Subscriber object to Ember
Adds post submit form to group view
Comments patch method, adds 'default' to feed case, replaces Group.destroy to FeedFactory.destroy
Adds opportunity to set timelineId for new submitted post
Adds 'manage' route for user's profile
Replaces /subscriptions/ to /subscribers/ for removing subscriber, adding and deleting admins
Add validation for admins actions
Adds validation for set post into custom timelines
Adds cosmetic changes to UI
Replaces validation from route to model
Adds feedInfo API route
Changes api route from feedInfo to feedinfo
Adds the very first version of responsive layout.