Fix #332 Add Translations support to plugins

Add Translation ability to plugins:
          # audio input plugins
          alsasrc
          audiotestsrc
          autoaudiosrc
          jackaudiosrc
          pulsesrc
          # audio mixer plugins
          audiopassthrough
          multiaudio
          # output plugins
          audiofeedback
          ogg-icecast
          ogg-output
          rtmp-streaming
          videopreview
          webm-output
          # video input plugins
          desktop
          firewiresrc
          usbsrc
          videotestsrc
          # video input plugins
          pip
          videopassthrough

Signed-off-by: Thanh Ha <thanh.ha@alumni.carleton.ca>