More Bootstrap / misc tweaks

This is a bunch of random tweaks, fixes, and visual changes.

* added "progress bars" to visually show percentages in compare-me modals
* added some success/failure feedback to the load button in Activecode blocks
* visual tweaks to the social media and search dropdown menus
* dynamically adjust the options available in the user account dropdown menu to reflect the the login status (e.g. change password link isn't useful if the user isn't logged in, etc)
* fixes #257.
* remove a bunch of unneeded files (I left behind a bunch of backup copies of the *.rst sources when I added tabbed/odd answers to the exercises.
* fixed a few tiny typos in the sources
* misc other visual changes