Cleanup CMake code
Remove things that are unneeded or already set by ECM
Use undeprecated variables
Enforce a minimum KF5 version
Make use of autorcc
Don't install desktop file with executable bit set
Remove things that are unneeded or already set by ECM
Use undeprecated variables
Enforce a minimum KF5 version
Make use of autorcc
Don't install desktop file with executable bit set