tags for changeset should be customizable

[flaimo]

when uploading a changeset, i now tend to add a source=bing or source=geoimage tag zu the changeset instead of each element. as it seems, josm doesn't remember the tags i last used and always just initializes "created_by" and "comment".

it would be nice if i could edit the default tags that get prefilled when uploading to a new changeset. another possibility would be if josm just remembers the tags used for the last upload.

version used: 4064