Replace HTML entities with real characters

Translations will have to be updated.
Let template mechanism escape HTML
Escape underscorejs templates

Use <%- … %> instead of <%= %> to render text.
Fix course index titles encoding
Encode section name in welcome back message
Escape graph labels in courseware progress
Update tests according to templating changes
Update capa tests

Apply the same template modifiers as in edxmako.
Update test templates to add `| n` modifier, when necessary.
Compare unicode strings in course about tests
Replace &hellip; with … in JS code

There should not be any HTML in translation strings.
Remove &amp; from checklist buttons

Unfortunately, this doesn’t fix existing courses since checklists
buttons’ labels are stored in the modulestore.
Remove all ellipses