Log Message:
librecad: Upgrade to 2.2.0 rc1

Exact changelog is unknown, but there is Qt4 -> Qt5 switch.

Upstream changelog
==================
2.2.0 Release Candidate
There were more than 250 commits since 2.2.0-alpha, thus it was overdue to get \ 
rid of the alpha in the tag now.
With some more improvements in the last couple weeks, we switch directly to \ 
Release Candidate as the response from community is, that the master branch is \ 
stable.
There are only some minor changes in the line before the final 2.2.0 release.