Match location preferences are too course

Currently the only options are "nearby" and "everybody". This is both fairly course grained and ambiguous.

Two alternate methods would be:
- A radial option for: "Show me matches in my: City, State/Province, Country, Everywhere"
- Let the user specify a maximum number of miles between cities (zero being noted as the same city).

The latter is easier to code; but, has a few more privacy concerns. Rounding the miles to one significant figure prevents stalking.

The issue names no files, tests, or entry points. First review how the existing “nearby” and “everybody” preferences are represented and applied, then resolve which proposed location model, distance units, rounding, and privacy rules are intended. Done means one defined preference behavior is implemented and its matching and privacy effects are verified.

Written by the indexing model from the issue text.