Small changes to clean up webagg javascript code a bit.
Added the nbAgg backend to allow interactive figures in the IPython
notebook.
Updates to make behaviour more consistent with other backends. Removed the throttling.
STY : PEP8 fixes
Merge branch 'nbagg_backend'

Conflicts:
	lib/matplotlib/rcsetup.py

Manually merged adding two backends (Qt5Agg and nbAgg)