Changed main layout for used with fragments. Added login view, item book view and the menu for order elements in the list
Added code for Login Fragment (without API Calls)
Added classes for use Retrofit lib(commented), but for now the app is using the Dropbox SDK
Added Events with Otto lib, and AsyncLoader for the epub list
Added EpubList adapter, Code for image loader  lib is commented
Added the API call and finish to connect all items. Right now List shows the ePubs stored in the dropbox account
Update README.md
Addes AsyncDownload for downloading the ePub, and code for retrieve the cover and the title of the ePub
Merge branch 'developer' of https://github.com/coffeearmy/Librarian into developer

Conflicts:
	README.md
Change Dropbox SDK login logic to a specific Fragment
Added Classes to see the books in a grid instead of a list
Added dialog for view ePub View, GestureListener for recognise double-click.
Added Comparators for order the list. Now the list shows all fields and is able to order by A-z and date
UI changes, added a progress bar for indicate the element is loading. Now if the ePub title isn't yet available the list order by filename.
Check if the ePub don't have title or cover
Now the app remembers if the user give access to dropbox. Added option for log out dropbox
Add fix to menu.xml and fix navigation between fragments
Found Bug in grid view changed with a staggered grid view lib. Fix Markdown in readme.md
Fix format Readme.md
Fix overflow menu doesn't show, now when a date can't be parsed it uses today date, checks if the user is logged to see the ePub list