generate-scenario: implement a url that generates a scenario

(not completely implemented yet)
pandemic-game.js: move where scenario id is generated
generate-scenario: save generated scenario to datastore
generate-scenario: automatically name it using current date
servlet: new endpoint for listing scenarios and getting specific scenario
cleanup: rename deal_id to scenario_id in some places
js: switch to use s/scenarios endpoint instead of s/deals

at least for scanning for new scenarios and downloading specific scenarios
js cleanup: rename more 'deal' variables to 'scenario'
localStorage: rename and document keys
pick_scenario: for scenarios named by a date, show the date
pick_scenario: show number of epidemics
generate-servlet: do not expect . in suffix
allow scenario ids to contain dashes and periods
make game_id distinct from scenario_id
player_setup: construct next url with game_id not scenario_id
fix: use game_id in url not scenario_id in more places
results page: allow scenario to have minuses and periods
resume_game: fix for changes in api
js: fix start_publishing_game()
generate_scenario: fix bug introduced in earlier refactoring