Minor changes

* Removes commented code
* Renames solo mode into "Playlists"
* Adds/rewrites some comments
Merge branch 'dev/solo'

Conflicts:
	src/ch/epfl/unison/ui/AbstractMenu.java
	src/ch/epfl/unison/ui/GroupsActivity.java
	src/ch/epfl/unison/ui/GroupsMainActivity.java
	src/ch/epfl/unison/ui/GroupsPlayerFragment.java
	src/ch/epfl/unison/ui/NfcManagementActivity.java
	src/ch/epfl/unison/ui/SoloPlaylistsActivity.java
Changes comments and explicits action bar visible menu items
Removes unused methods, avoids usage of mMAinActivity from AbstractPlayer

* AbstractMenu
Adds FLAG_ACTIVITY_REORDER_TO_FRONT for solo mode

* *PlayerFragments
Each specialization uses his own HostActivity instead of Abstract.MainActivity
(avoids explicit castings)
Moves playlist mangement from Abstract to Groups player

* Playlist management
The whole logic about handling a playlist (pick next/prev track, etc.) is
moved to the specialized implementation. Required method (next/prev, etc.)
from Abstract are thus set as abstract.

* Getters/setters
Comments unnessary getters and setters, replaced by direct access to instance
variables.
Oragnizes imports and formats project
Displays only playlists created with GS

* SoloPlaylistsLocalFragment
Displays only the playlists created with GS.
Organizes and formats project
add new grouprecommendation features
change icon for group history
Merge branch 'NFC'