Show the installed application source in the details view

This matches the new mockups from Allan, although requires PackageKit from
master to return correct results.
Load the GNOME moduleset from a file rather than hardcoding

This allows us (or vendors) to modify this list without recompiling the
application and will also allow us to support package-based core modulesets
in the future.
trivial: Center the infobar content in the window
Load a core moduleset from a file

This is intentionally incomplete at this point; more research required.