a bit more grouping in the validator tree

[Klumbumbus]

Some validator tests print the affected tag and could therefore be grouped to clean up the validator tree. To avoid too much groups (too much clicking to finaly see the affected object), this should be done only for common mapping errors. I suggest groups for:

• deprecated tags ("{0} is deprecated", "{0.tag}")
• unconnected nodes ("{0} must be connected to a way", "{2.tag}")

[Klumbumbus]

In 11138/josm:

fix #13804 - group deprecated tags and isolated nodes in the validator tree