build: replace Gtk deprecated calls
window: handle key pressed properly

Before the code handling key presses was an unreadable mess. Now we use
gtk_accelerator_get_default_mod_mask as stated on Gtk documentation.
search: added initial search implementation
build: remove unused c/css code
event-widget: render locked state of the calendar
views: use GcalEventWidget API for locked sate
window: sync search-view hiding with stack transition

The previous approach was causing an error on the animation code of
GtkStack because the search-view's GdkWindow was banishing before
the end of the animation.
misc: updates to code style and docs
window: shorten stack transition duration
month-view: optimize set :date property

There's no need to calculate first day of month date twice.
utils: retrieve first_weekday from locale

Bug: https://bugzilla.gnome.org/show_bug.cgi?id=703317
month-view: add first_weekday settings to view

Bug: https://bugzilla.gnome.org/show_bug.cgi?id=703317
week-view: add first_weekday setting to view

Bug: https://bugzilla.gnome.org/show_bug.cgi?id=703317
year-view: launch edit dialog on event activate
misc: code style and comments removed
window: set timezone of date when moving to today