Keep track of prior searches

Should associate prior searches per searcher (including customize searcher)
* Suggest putting them by searcher name and index path (this way if index location changes or search name change, could still match up based on other value)
* Store in separate file from settings.xml, but in same State directory
* Add a dropdown command to the View toolbar

Ideally mimic regular Eclipse search prior search dropdown functionality

Start by locating the searcher handling, settings.xml, and the State directory, then inspect how the View toolbar commands are defined. Compare the requested behavior with Eclipse's regular search history dropdown. Done means prior searches are associated with the searcher name and index path, persisted separately from settings.xml, and available from the View toolbar.

Written by the indexing model from the issue text.