Remove sound effects (except the one for push notifications)
Remove observers on contentOffset

After removing sounds on #448, these observers did nothing, so let's
kill all that dead code
Removed option to disable sound effects
Merge pull request #456 from wordpress-mobile/issues/448-remove-observers

Remove observers on contentOffset
Merge branch 'develop' into issues/448

Conflicts:
	WordPress/Classes/WPTableViewController.m
Merge branch 'issues/448' of https://github.com/wordpress-mobile/WordPress-iOS into issues/448

Conflicts:
	WordPress/Classes/WPTableViewController.m
Merge pull request #449 from wordpress-mobile/issues/448

Remove sound effects (except the one for push notifications)