Bring back per project settings of cmake executable

Summary:

This patch brings at least part of the functionality back that was removed in commit b9a746480f11b310b0c6e9a3e3d9ab795874b695.

This means that one will not be able to choose cmake executable when creating a new project, but it is possible to set it per project under the advanced settings.

Reviewed By: apol

Differential Revision: https://phabricator.kde.org/D7762