Install D-Bus interface files in $(datadir)/dbus-1/interfaces

- Rename D-Bus interface files according to the recommended scheme

- Install D-Bus interface to $(datadir)/dbus-1/interfaces, as specified
  on the freedsektop website[1].

Installing interface files on the system will allow for compiling LRC
without having to duplicate the D-Bus interface files.

1. https://dbus.freedesktop.org/doc/dbus-api-design.html#interface-files

Change-Id: I687484aad2d1e4bb27553db76018ffb6efc52bbd
Tuleap: #688