devel/plasma: Update to latest snapshot and undeprecate

Upstream has no yet adapted the code to use PyQt5 instead PyQt4. Thus the
option MEMMAP that requires Qt4 has been completely removed to make the
removal of Qt4 in the ports tree somewhat easier.

While I'm here:

• Fix license
• Simply GitHub usage by removing GH_PROJECT
• Add a patch to fix an issue with fake headers (not merged into upstream's repository, yet)

Approved by: miwi (mentor)
Differential Revision: https://reviews.freebsd.org/D19395