Post GSoC Additions

Additions or Modification made after GSoC:

1. GUI improvements in the standalone version
   
   • Selection contour
     
   • Center images
     
   • Checkered background
   
   
2. Algorithm improvements
• Modified Graph Construction from Kolmogorov et al's What Energy Functions Can Be Minimized via Graph Cuts?
• Modified data and smoothness term to improve speed
• Modified edge capacity datatype from float to int


3. Synchronized with trunk (only required resolving CMakeList.txt conflicts)

Upcoming changes:

1. Write out the mask in the pto file
2. Port GUI updates from standalone app to hugin
3. The ImageCache doesn't support loading alpha channel from the original file. The transparent parts are black. This needs to be fixed.
4. Fix a crash in hugin when changing masking algorithms