FIX some warnings and potential bugs found by FindBugs
Minor changes on many classes for handling playlists
FIX fetchings playlists from gs in-app DB
Adds doDELETE with postpone delay
Introduces buttons on HomeActivity

ListViews are repalced by buttons with icons.
Class reordering and renamming
FIX NullPointerException
Solo player can play songs from the playlist.

The SoloMainActivity retrieves a playlist from the android database. The player
itself does not hold the playlist. The PL is stored in the SoloMainActivity,
since it will be shared with the SoloTracksFragment. This way, it will allow
modifing the tracks order on the fly, during lecture (but this is "musique
d'avenir").
All the lecture stuff (next/previous/etc.) is done inside the PL object.

AbstractPlayerFragment: explicits the both app modes (groups, solo) by using an
enum (solo mode doesn't use the mHistPointer, since the playlist is completely
known before lecture).

Misc:
* Removes moved files (old locations)
* Removes unused solo_player.xml
* Organizes imports
Overall changes and improvements

* Adds shuffle support in PlaylistItem
* Organizes imports
* Renames some abstract classes
* Creates empty SoloPlaylists*Fragments for later implementation
* Improves AbstractListFragment handling
* GroupsRatingsFragment uses generic list layout, such that the specific layout
  could be removed
* Relabels and adds android ids to some layout elements
Applies android formatter
Commit before pull (don't remember the changes made)
Merge branch 'dev/solo' of https://github.com/lca4/unison-android into dev/solo
SoloTracksFragment: displays tracks of playlist
FIX Group History menu appears only when needed

Group History is invisible by default (defined in menu.xml).
Visible in:
* GroupsActivity
* GroupsMainActivity
Sets GroupsMainActivity launch mode as singleTop
FIX home button misbehaviour

* If still on HomeActivity, doesn't close the app
* If in GroupsMainActivity, leaves the group
HomeActivity extends SherlockActivity

Instead of AbstractFragmentActivity, which was not suitable since the Home is
not intended to host fragments.
FIX missing menu on HomeActivity
Merge branch 'dev/solo'

Conflicts:
	AndroidManifest.xml
	res/values/strings.xml
	src/ch/epfl/unison/ui/GroupsHistoryActivity.java
	src/ch/epfl/unison/ui/GroupsMainActivity.java
	src/ch/epfl/unison/ui/HomeActivity.java