Fix icon conflicts

Trello: https://trello.com/c/0UAxh0kY
Fixes: #1470 

This pull request:

* Uses the new `h-icon-` namespace for all icon fonts.
* Separates application styling of icons within components from the icomoon class names.
* Small markup fixes in the markdown template.
* Namespaces the "pushed" class in the annotator toolbar plugin.
* Cleans up some convoluted css output in the inject stylesheet.