validate-launcher: restructure filesystem

https://bugzilla.gnome.org/show_bug.cgi?id=739091
launcher: Don't implement product-specific TestManagers.

This manager will be moved in GES.

https://bugzilla.gnome.org/show_bug.cgi?id=739091
launcher: add a way to specify an application directory.

https://bugzilla.gnome.org/show_bug.cgi?id=739091
validate-utils: downgrade ERROR to DEBUG.

This function is called in places where it is legit for it
to return NULL.