Removed deprecated wakelock dependence from Android backend

Since the wakelock methods we use are deprecated, I looked into the possibility of alternatives without breaking 1.5 compatibility. This solution mimics the same behavior on the screen and is recommend to be used instead. (See http://developer.android.com/reference/android/os/PowerManager.html#FULL_WAKE_LOCK ) 

Note: I did some basic tests, but I didn't go super in depth so this could use some more testing.

Some benefits: 
- Wakelock permission no longer required to use
- Now handled directly by Android system
- Removes the use of some deprecated code
- Google recommends this method as an alternative (See http://developer.android.com/reference/android/os/PowerManager.html#FULL_WAKE_LOCK)