Support calendar events on Pebble Time timeline

[smokku]

pebbled should pull events from calendar and put them on Pebble Time timeline

[smokku]

@smurfy toyed around calendar at smurfy/fahrplan#168

[smurfy]

only with writing and listing calanders, but listing events should work too

[javispedro]

I also have some code to list events (inc. recurring) from the Sailfish calendar for my Toq manager: https://git.javispedro.com/cgit/saltoq.git/tree/saltoqd/agendamanager.cpp

I was planning to put that on the smartwatch shared library too, but since it's extremely simple to actually list the events (most of the code there is formatting them for the Toq)... prob not worth the effort.

By the way, if no one's done it by then, by the end of august I can try to get a look at the new "timestream" protocol and implement support for it in pebbled. EDIT: Sadly I take this back, no time :(