Trebuchet: Add 5x6, 5x7 and 6x6 default workspaces

  Had a 5x6 grid (with 6 hotseat spots) on my fajita back in los 16.0
  and wanted one on los 17.1
  On my Shamu I used to have 6x6 (with 6 hotseat spots)
  5x7 has 5 hotseat spots

Change-Id: Ib8d5dcc70d386376755c0a57b009ced1b2ee0834