Initialize to activated date when adding w/o quick-add: Bug #732029

When the user doesn't supply quick-add details but goes straight
through to the editor, initialize editor with initial date/time.
Crash due to altering stack model cache during iteration: Bug #732035

The stack model map was being altered via our own signal handler
being fired due to destroying widgets while walking the cache map,
causing an assertion in Gee.  Using a copy of the map's keys works
around the issue.
Switch Idle and Timeout code to use Scheduled class
Generate recurring instances when added/discovered: Bug #732043
Create recurring events with Quick Add: Bug #725785

Quick Add parser now accepts keywords for creating recurring events.
This patch also introduces code for interpreting and generating
iCal recurring rules (RRULE) and associated tests.
Ensure day-spanning events sort to top of Month cell: Bug #732224
Prevent double-adds when modifying event

Due to recent change generating events when a recurring event is
added, it's possible to alter an event significantly (i.e. from an
all-day event to a timed event) that it's reported as added twice.
This patch catches the second add and stifles it.
Better responsiveness when performing I/O: Bug #725769

Now using EDS async variants wherever possible and a busy cursor over
the window while the async operation is at work.
Deal with standalone punctuation in Quick Add details

For example, "Alice & Bob".
Add "this" to TIME prepositions

Allows for [Meeting this Thursday]
Additional tests and fixes for Quick Add parsing

Discovered while working on Quick Add documentation.
Fix regression preventing recurring events from gen'ing instances

Recurring events were not generating all instances.  This was fixed
in commit ad99022.  However, this bug was reintroduced when the switch
to async I/O was introduced (commit c5d3b5c).  This patch re-fixes the
problem.
valac-0.22 -> valac in debian/control

Primarily for our Daily Build PPA, it appears valac-0.22 has been
removed from Utopic with 0.24 taking its place.  0.24 isn't available
for Trusty, so to avoid separate control files, just require the
valac metapackage meet our version requirements and leave it at that.
Updated German translation
Don't pass non-null Value messages holding null

It's a pain for the Toolkit.Cards to have to check for non-null
Value messages holding null references, so Toolkit.Deck will "strip"
those messages out and simply pass null to the Card.

This occurred because apparently either GSignal or some Vala-generated
code was turning a null Value into a non-null Value holding null and
the code on the other end of the signal wasn't expecting that.
Updated Spanish translation
Updated Hungarian translation
Updated Hungarian translation
Updated Polish translation
Improvements to the California.Iterable class and helpers