language-manager: Add rust to the list of languages

https://bugzilla.gnome.org/show_bug.cgi?id=722721
indentation-c-style: enable the plugin for Rust files

https://bugzilla.gnome.org/show_bug.cgi?id=722721
dir-project: Add Rust *.rs files to sources.list

https://bugzilla.gnome.org/show_bug.cgi?id=722721