Add Account and FileSystem base classes

Also implement Local, Ext SD and Dropbox file system classes
Make DropboxAccount extend Account
Add Account list and make AccountsActivity a ListActivity
Add FileSystem.isEnabled() and override for ExtSDFileSystem
WIP: File system changes
Add graphics for local/sd filesystems
Show filesystem icons in VolumeList
Fix fsType logic in VolumeListActivity
Add icons to FS dialog in VolumeListActivity
Add note about filesystem ordering to EDApplication
Nuke EDApplication.getDropbox()
Increase height of fs dialog items
Bump up to API level 14
Use FS icon in the ActionBar
Get rid of ActionBarHelper
Don't put FS name in FileChooserActivity title
Fix README.md to mentioned DropboxAccount.java
Use LayoutParams.MATCH_PARENT instead of FILL_PARENT
Use SuppressWarnings for PowerManager.FULL_WAKE_LOCK
Increase padding on FS dialog items