Add tree (and plot)

* "Add Tree" button activates addTreeMode
* User must click the map to set the initial tree position (soon they will instead enter an address or click a geolocate button)
* User must then drag the tree to desired position
* Then the tree fields are enabled for editing
* In the end I did not use "inlineEditForm.js" because I have only edit fields (not display fields)

We update the map when adding a tree:
* Endpoint returns new geoRevHash
* If geoRevHash has changed, JS updates layer URLs and redraws