Stop blowing up names of array properties in editor pane.

The JSON Editor marks these up as <h3>s; we style 'em here to have
(pretty much) the same size and weight as the normal labels it uses
for simpler properties.
Be more aggressive about disabling dragging on deselect.

Due to a leaflet bug, we need to disable dragging *before* calling
setIcon.

http://stackoverflow.com/questions/22671733/why-doesnt-marker-dragging-disable-work
"Delete" functionality, and tests.

As planned, works by sending 'selectedFeatureDeleted' and
'selectedFeatureUndeleted' events, which gray the marker and set
a "deleted" flag on the feature itself.