Minimap enhancement

[danieldegroot2]

Improve the minimap (miniature map view in the bottom right), to be more similar to the ones in the iD editor, Mapillary etc..

• Make the minimap dynamic: zoom in relative to the users viewed area on the large map view. I do not see many use cases for the current static minimap (ease of going to a specific location is limited by the low zoom level, instead search would need to be used).
• Add a button to zoom out to the full map; this will bring both map views back to the default zoom level.
• Make the minimap collapsable, so it does not get in the way when viewing imagery.
• Make the minimap resizable.
• Make the background of the minimap selectable (main layer choices +- the selected imagery).
• Add a marker on lower zooms to indicate where the selected imagery is.

(two of these are not currently in iD, see iD/issues/5415)