This makes it easier to read, because we do not have to handle a list of
files that get added to the targets. In other KDE projects, we also
prefer the target centric approach.
In case one wants to reuse the same category in multiple places, it
would be best to create a small static lib. But for now, this is not
needed.
We use kdeconnect-version.h in several places and therefore it needs to be in the include path. We currently do this by setting target_include_path in a few places. Replace this with an interface library that we can link against that sets up the correct include path. IMO it is cleaner this way.
Summary:
* cmake 2.8.12 is really outdated, 3.0 is minimum in plasma & kf5
* cmake_minimum_required should be at begin of toplevel CMakeLists.txt
* bump qt version to 5.7, matching the min Qt version of kf5 5.42
* with ecm being part of kf5 since early versions, share ${KF5_MIN_VERSION}
* use QT_MIN_VERSION & KF5_MIN_VERSION also for separate find_package calls
* deduplicate all KF5 components searched for in unconditionally included
subdirs
Test Plan: Still configures and builds with all options OFF & ON
Reviewers: #kde_connect, nicolasfella
Reviewed By: #kde_connect, nicolasfella
Subscribers: nicolasfella
Differential Revision: https://phabricator.kde.org/D11418
