Changes to footage information panel

- Display additional information about channels
  and buffer type (float/byte).
- Don't show frame number beyong sequence length.
- Also fixed issues with footage length calculation,
  so it's pronbably will be needed to reload some
  of existing footages.

git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@56626 954f8c5b-7b00-dc11-b283-0030488c597c