Convert all anchors to spans so clicking them does not change the URL

This is especially useful for Client-side apps that rely on browser
routing
Merged from master
Removed extraneous .preventDefault calls

The only ones left are on form submission. Form submission is done so
Enter can be pressed in modal dialogs
Merge remote-tracking branch 'origin/anchors-to-spans' into testing

Conflicts:
	src/plugins/oer/assorted/lib/link.js
	src/plugins/oer/math/lib/math-plugin.js