Start KF5 transition

Add ECM and comment out things that are going away.
Exclude platform theme plugin from the build

This might be used later, for example to provide QML based common dialogs
instead of the KDE implementation but all has yet to be figured out.
Remove data providers

Plasma already has data engines.
Remove the old shell

We are going to use plasmashell instead.
Remove daemons

Plasma has a notification daemon and PolicyKit agents, we should
contribute to them.
Remove screen saver

We no longer want a screen saver because it's better to turn off the
monitor and save some power.
Exclude Weston plugin from the build

Keep the code a little longer for reference but this is going to die
soon.
Exclude declarative components from the build

Need to figure out what to do with these.
Exclude shell styles from the build

Need to figure out what to do with them.
Exclude packages from the build

Keep the code for reference but should go away pretty soon.
Install SDDM theme from look & feel
Install look & feel package
Remove containments and elements translations
Remove scripts
Remove useless header