Added vksdk_library

Modified vksdk_library: added method to logout wihtout UIHelper Activity
Added picasso library (need to test autocache function)
Made basic app structure (fragment navigation etc)
Added Login/Logout/SaveSession feature (access_token is saved in SharedPreferences)
Added Feeds feature (basic poor functionality)

TODO:
- Detailed post view
- Parse and display VKAttachments JSON
- Parse and display copy_history field (array)
- Load new elements, next elements
- onConfigurationChanged cache and display list
- Refine feeds_item.xml view position, size etc
- Date display in feeds - refine