Remove SOTM US from the banner rotation

Remove SOTM US image from the from the front page banner rotation, leaving
only main SOTM and server donation drive ads.
Add a reopen API call for notes
Allow notes to be reopened from the web interface
Fix overlapping text in markdown help
Keep the map visible as the changeset page is scrolled
Force notes list to be realised in notes#mine

There is a rails bug which means that using count on a relation
that uses uniq and offset/limit and which hasn't been realised
yet will always return one, so force it to be realised.
Update mailmap
Make note metadata consistent in the GPX output format
Use note.closed? in a consistent way
It's <br> not </br>
Switch from content-box to border-box for layout
Layout cleanup
Stop the richtext help wrapping
Merge branch 'master' into groups-sketch
Groups: member list can be edited