Map viewer should have better/configurable initial selection

[kingjon3377]

The map viewer has a default selection of "the invalid point", (-1, -1). This is confusing, and awkward for usability. There should be a better default (the player's HQ?), and probably some way for the user to specify it. Maybe it should be stored in the map. If we ever get "configuration storage" support, this should be stored there.

The view should start out centered on the initial selection.