package selection by checkbox, change accordingly project.vala
Merge pull request #110 from inizan-yannick/master

Use combobox to add (multiple) new packages. Thanks to Yannick Inizan!

Runtime of selecting ("commiting") new packages is always O(n) (where n is
maximum number of packages). This shouldn't be an issue because there aren't
too much packages but can be improved by keeping a list of selected packages
with O(mlog(m)) performance costs by inserting/deleting (where m is number of
currently selected packages) and O(1) costs with "commiting" new packages.
Run SymbolBrowser update only once when multiple pkgs were added.
Guanako: Don't crash on circular deps, keep ordering of deps. Closes #113

 * No performance optimizations. get_package_dependencies_int could include
   package_name in deps list to save some runtime performance. Additionally
   add_packages code could be cleaned up. Shouldn't be a bottleneck though
   because package list + deps are not that big.
 * datatype_to_string: Track InvalidType with conflicting vapis.
   Currently no hint on user interface.