Add search function

So far you have to run around the map with your cursor or finger, there's no way to search for a given term to be taken there.

The issue names no file or test; start by locating the map view and its current navigation entry point. Determine how a user should enter a term and be taken to the matching location, then verify that searching for a given term reliably moves the map there.

Written by the indexing model from the issue text.