Plasma 5.13 beta release preps

[Jonathan Riddell]

Plasma 5.13 beta is out in 3 weeks and 5.13 final out three weeks after that.

https://community.kde.org/Schedules/Plasma_5

https://phabricator.kde.org/calendar/query/month/2018/05/

I'm the release manager for the beta and Bhushan is going to do final.
The beta tends to get more press coverage than the final.

We've started a wiki with stuff for the announcement at
https://notes.kde.org/p/plasma_5_13

Let me know what Promo wants to do for the releases

Jonathan