[PATCH 14/15] comctl32/monthcal: Fix control placement

[Nikolay Sivov]

Changelog:
   - fix control position in client area - it should be centered in it, also simplify some
     rectangles calculation
   - hittesting heavily relies on rectangles dimensions and position, currently hittest tests fail
     cause first positioning is wrong and second multicalendar mode isn't implemented at all, so
     fix tests accordingly