Don't stack up OSM Notes (better called "Map Notes")

Currently it can easily happen that users edit an updated POI description. Since OSMyBiz store POI updates (and "other" categories) as an OSM Note Issue, currently another OSM Note Issue is inadvertedly stacked up at the same place. Instead OSMyBiz should add a comment to the pre-existing OSM Note Issue.

In order to let OSMyBiz detect already existing OSM Note Issues - at least for the same user - OSMyBiz probably has to store the OSM Note Issues (by id) similar to how it stores Nodes in it's own user database.

BTW: OSM Notes are better called "Map Notes" to distinguish them from Nodes.