Menu: Improved sloppy menus logic

Instead of relying on fixed angles, we now test that the current
mouse position is in the triangle defined by the previous mouse
position and the submenu's top-left and bottom-left corners. The
sloppy timer duration has also been increased to 1s.

Change-Id: I575346ac20b5da68ab8ebd6e3cf9a6ddba2b7a72
Reviewed-by: Jens Bache-Wiig <jens.bache-wiig@digia.com>
Reviewed-by: Caroline Chao <caroline.chao@digia.com>