Turn: Use attr_reader where possible

Moar safety
Turn: replace reactions accessor with reacted_players

More safety because someone could edit the hash if using a reader
Turn: Take decision type in make_decider

We always set the two things together anyway, so this allows removal of
another writer
Game: Use attr_reader where possible
Player: Use attr_reader where possible
Character: Use attr_reader where possible
Action: Use attr_reader where possible
Game: Remove $player_count global
test: Move 1-influence Embezzle setup into a context
test: Add test for 1-influence Duke embezzle
test: Move Embezzle tests into contexts

Planning ahead for more tests
Allow player choice in responding to forbidden challenge

Previously, the bot would automatically select to flip all cards if
player did not have, or flip the forbidden card if player had.

However, if player has 2 influence yet does not have the forbidden
character, it is still a valid option to flip a character anyway!
This means we need to allow a "!flip all" command.
prompt_challenge_defendant: Inform of !flip all if applicable