Bug 965869 - http/2 draft 10. r=mcmanus
Start (maybe finish) refactoring/simplifying padding handling.

This may or may not actually work, but hopefully it will, because it's
WAY simpler than the old way of doing things.
Lay out huffman tables better for memory savings
Add more logging around padding handling
Initialize mPaddingLength in the proper location
Don't try doing padding handling if there is no padding
Fix up logging arguments
Add logging for discarding
Properly set things up when processing data frames that are all padding