Allow removal and adding of new packages over UI.
Replace deprecated Map.contains with Map.has_key.
cmake: Distinguish between libs to link and to check. Closes #39

 * Extend cmake integration and cmake code itself (ValaPkgs):
   Support {nolink} and {nocheck} options (and combinations {nolink,nocheck}).
    - nolink: Do not compile with cflags and libs.
    - nocheck: Do not check with pkg-config (implies nolink).

   Manually added packages have no option but the nocheck option will be added
   if there is no .pc file for those packages (exact_package_name.pc).
   Packages added as dependency of manually added packages have the option
   nolink except there is no .pc file. In that case the nocheck option is
   added.

 * List all packages in cmake/project.cmake.
Synchronize cmake buildsystem data files.