Apply 'n' filter when data shouldn’t be HTML encoded

There are some temporary fixes in this commit: all the HTML entities
should be removed from translation strings (e.g. &amp;), real characters
should be used and translations updated.
Remove unneeded 'h' filters from templates
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