Much faster table of contents.

Fixes issue with toc jumpiness near bottom of articles.

Fix for web view scroll delay.

Much better handling of TOC show/hide swipe.

Now angle and speed of swipe is tunable. Works better with
html tables which have overflow x scrolling also.

Fixes for mutate-while-iterating bugs.

Change-Id: I06debfb01baad1bf03ed1cf6c9af41f0a835e56e