Exhibition page improvements

[sammeltassen]

WIP

• Remove 'read more link' on text block if no annotations are available
• Indicate video modals on exhibition overview page (with an icon for example)
• Remove fixed position of title block (needs page redesign for title placement)
• Allowing html in text blocks and captions (for links and emphasis)
• Change style of text modal (size and background color)

[stephenwf]

I think some of the bugs have been addressed in the new static site, but not any changes to the design. (You can also have HTML in most text elements now, and if not it's a 2 second fix on a case-by-case)