Add Node.Feature() for simpler GeoJSON conversion
Fix GetNode() in database.go

Previously, it was referring to the no-longer-extant column 'email' in
nodes_cached. This replaces that with an empty string.
Add GeoJSON support for /api/node

Close #39
Implement node dumping by date

At /api/all, if one specifies a RFC 3339 timestamp as the contents of
the "since" http form, only nodes that were updated or retrieved from
another map more recently than that time will be dumped.

Close #3
Add somewhat untested plain SMTP auth
Reverted marker-icon and added inactive-marker.png
Merge branch 'development' into f.nodemarkers
Fix up markers and conform to style