Reload tiles when adding a tree

A regression occurred when adding map features. The main issues is that
the geo rev count is updated by a database trigger, thus invalidating
any existing objects. Since we want to return the update geo rev, we
need to requery the instance.

Fixes #1152
Merge pull request #1163 from OpenTreeMap/fix/1152/reload-layer-on-add-tree

Reload tiles when adding a tree