Auto-pay mana cost options

Enable the user to auto-pay for mana costs:

- [ ] - "Dumb" version: arbitrarily select mana sources that could pay with no optimization (use a Reflecting Pool to pay for generic when colorless sources are available
- [x] - Mana pool version: Use mana of the same type if it exists in the mana pool (and an optional override to use colored mana for colorless), but user selects any unpaid cost manually
- [ ] - Advanced version: Uses mana from the mana pool first, then selects sources somewhat intelligently (ex. use colorless-only sources first, then sources that only produce 1 color of mana, then 2)
- [ ] - PowerUser version: User can select arbitrary rules for priority in mana sources, such as:

1. Use mana from the mana pool of the matching color
2. Use remaining colored mana in mana pool to pay for generic*
3. Use artifact sources that don't have side effects
4. Use lands which don't deal damage to me
5. Use artifacts with side effects
6. Use lands which deal damage to me
7. Use creatures sources

PowerUser version would obviously take more resources and planning

No files, tests, or entry points are named. Start by locating the mana-payment and mana-pool handling entry points, then compare the checked-off mana-pool behavior with the proposed dumb, advanced, and PowerUser options. Done should be defined as an agreed implementation scope and corresponding behavior.

Written by the indexing model from the issue text.