UI improvements; fixed bug with 'Show x more' functionality

- Users can now double click on a calendar square to open the quickpost
dialogue
- The '+' button is styles to be less intrusive
- The '+' button now only appears after half a second of hovering over
a calendar square
- The '+' button no longer sits on top of post titles in calendar
squares with many posts
- The 'Show x more' functionality for calendar squares with many posts
is working again