Release calendar

[Jonathan Riddell]

I've added the release dates for Plasma 5.12, .13 and .14 as well as
Frameworks releases to the end of the year onto the calendar on Phab.

https://phabricator.kde.org/calendar/

Which makes more sense than the Google calendar I had on my personal
account.  You should be able to export the .ics and import it into
whatever calendar you like to use.

Jonathan
Not the boss, not the chief and not secretly controlling the whole KDE
release process