Introduce SDDM components. Port all themes to the components.

Now all themes share same basic components. Components have two
different versions aligned with QtQuick versions. Depending on
the qt version compiled with, either version 1.1 or the version
2.0 of the components are installed. Themes are also configured
during installation to work with the installed version of Qt and
SDDM components.

This commit also merges elarun and maui themes which previously
residing in the sddm-themes repo. Since components are shared
we can host a couple more themes in the main repo.