This is also made a QML singleton that will be used for the applet
config view where it will add the plugin configs once we add that
possibility.
The same instance is then set to the DaysModel from QML.
REVIEW: 125951
This adds a simple plugin interface that can be subclassed
and provide events integration with Plasma Calendar applet.
It's asynchronous and I've kept it deliberately simple.
For now the Calendar tells the plugins which date range
is being displayed, the plugins load the data and then
emit the dataReady() signal containing the events.
The events are stored in a multihash for quick access
by the Calendar's agenda part but also for overall
easy-to-use (eg. in teh model data()).
The event data is stored in EventData class, which has
a pretty self-explanatory members, except perhaps the
"isMinor" property. The intention with this is to support
namedays, where in some countries the calendars have
different name every day. This is just a minor holiday
and as such should not mark the calendar grid, otherwise
the whole grid would be in a different color.
Putting the interface here might raise the question of
depending on plasma-framework, but plugins provided by
KDE can go to plasma-workspace and other 3rd party ones
would just have to live with it. I don't think it will
be a problem but if it turns out it is, we can rethink
the placement.
REVIEW: 125817
CCBUG: 349676
CHANGELOG: Allow plugins to supply event data to Calendar applet
This reverts commit fa2109ccb6.
Turns out the plan to raise the version with every framework
release is not as simple as raising the version numbers as
this breaks pretty much everything.
