Student Notes UI

This work is for [TNL-932] (https://openedx.atlassian.net/browse/TNL-932)

@polesye Ping me with any questions, please.

CC'ing @talbs @explorerleslie 
When do we need to add ellipsis at the beginning and at the end? 
What should happens if I click on `<a href="" class="note-excerpt-more-link">More</a>` ?