Reorder a bit the top of the CMakeLists.txt to be more similar to other frameworks

Summary: Mainly not require the same ecm that the version but -1 and use the same naming for the Qt variable so when the scripts update it to a newer version it gets updated properly

Reviewers: dfaure

Reviewed By: dfaure

Subscribers: dfaure, vkrause

Differential Revision: https://phabricator.kde.org/D24323