Clean up link interfaces of KDevPlatform libraries
Test Plan:
Created helper files including all headers per library and linking against
the library to test which libs need to be in the public link interface.
All normal & playground plugins still built against KDevPlatform.
Reviewers: KDevelop, apol
Reviewed By: KDevelop, apol
Subscribers: apol, kdevelop-devel
Differential Revision: https://phabricator.kde.org/D10696