Add ecm_set_deprecation_versions cmake function
Task: https://phabricator.kde.org/T15109
This will make setting the deprecation versions easier, otherwise one would need to edit the hex value. It also helps to keep the required versions and deprecation versions in sync.
Also this allows one to keep the deprecation warnings, when one excludes deprecations for a specific version.
Additionally the deprecation version can be overwritten by a cmake parameter. This will make local testing easier, because one does not need to edit the CMakeLists.txt files.
Edited by Alexander Lohnau