Namely, don't recompute layouts, as they do not change.
(The gyro codepaths were already doing something similar.)
* Keep ConfigDialog, FileManagerMenu & ReaderMenu open on rotation.
(In practice, only ConfigDialog is affected, as *Menu doesn't handle the rotation event.)
* Plugged an instance leak in the aforementioned Menu classes.
* Unify behavior & code with the gyro codepaths.