Removing deprecated usage of SCREEN_BRIGHT_WAKE_LOCK

Replacing the deprecated usage of SCREEN_BRIGHT_WAKE_LOCK
with the flag FLAG_KEEP_SCREEN_ON.

This made it possible to remove the permission
android.permission.WAKE_LOCK from the manifest.

Also removed some unused import statements.
Merge pull request #9 from tompen/remove_warnings3

Removing deprecated usage of SCREEN_BRIGHT_WAKE_LOCK