plasma/*: upgrade to 5.14.4
This MR upgrades Plasma from 5.13.5 to 5.14.4 which is now possible due to having Qt 5.12. We can't test it properly right now as Plasma Mobile won't show up (this happens even on current 5.13.5), but Bhushan suggested I should make the PR anyway. Everything compiles fine and at least kwin
seems to run fine (I can launch applications via SSH which show up) on x86_64.