Update style of post-fit plots

 - remove H->tt text from top label
 - increase size of CMSPrelim text from 0.03 to 0.04
 - Move the channel and category text to below the legend on
   the right (apart from ee and mm)
 - add new category names
 - increase size of legend and change position slightly
Merge pull request #243 from ajgilbert/postfit-plots

Update style of post-fit plots