Allow reverting way to previous state in history

[bilbo]

In Potlatch, you can press 'h' to see history of way and revert the way to previous version. In JOSM you can see history of way - with all its tags and list of nodes, but it have two drawbacks:

• You see list of node in a table, which does not give you much idea about where the way is/was in the map.
• You can't revert the way to previous version.

It could be nice to have some "revert" button when viewing each revision in JOSM, that will revert way and all its nodes to some previous state (given specific date/time or version of way).

History of all nodes in that way can be retrieved and then all nodes can be reverted, if they had different coordinate/tags at the given time.

This may also serve as the preview in worst case - you can revert the way to see the shape it had in the past and then just press CTRL+Z to undo the revert.