[RFC][Patch] Allow matching by object history in search function

[Woazboat]

​https://github.com/JOSM/josm/pull/80
​https://patch-diff.githubusercontent.com/raw/JOSM/josm/pull/80.patch

Added the was keyword to the search function to allow matching objects based on their previous states. I.e. was <expr> matches an object if <expr> matches any previous version of the object.

Example:

• was building=* to search for all objects that either currently have a building=* tag or have had this tag at any point in their history.
• was building=* -building=* to search for all objects that previously had a building=* tag which was removed at some point.