Fix adding files in ProjectBrowser
    instead of switch of path indices, use a custom TreePath with an enum as path_type for retrieve added document type.
When glade file is added, allow only ".ui" as extension.
Merge remote-tracking branch 'upstream/master'
Build library projects with CMake buildsystem.
fix .pc file construction in CMake buildsystem.
Update files for GtkSourceView 3.13.90 or newer.
Update files for vala 0.28.
Build Valama with webkit2gtk-4.0 if exists.
Merge pull request #158 from inizan-yannick/master

Libraries in cmake, code style fixes, vala version update, some fixes