week-view: added current day highlight

Cleaned code a little bit. Removed unnecessary instructions. Added style
class to handle current day.
views: fixed docs style
week-view: take into account GNOME time format

Bug: https://bugzilla.gnome.org/show_bug.cgi?id=703321
month-view: optimized, organized ::draw vfunc code
Revert: month-view: fix cell rendering glitch

This was not the proper fix.