Shorten long comments and add Read more...

[RoukePouw]

https://github.com/PlanBCode/hypha/issues/361

Longer comments get cut into a (html-less) stub (to prevent broken html) and appended by a 'read more' button.

[matthijskooijman]

Ok, all comments have been adressed. I've additionally made a few more small changes:

• Rebase on master
• Fix some style issues
• Add CSS classes
• Use "" instead of '' so \n is actually interpreted correctly.
• Remove <br/>, this can be done in theme CSS if required

With that, I think this is ready to merge.