Refactorings

The list of stuff remaining to complete the PR at https://github.com/bisq-network/pricenode/pull/7

Document provider implementations w/ links to API docs, etc
Add integration tests
Document / discuss how operators should (ideally) operate their pricenodes on a push-to-deploy model, e.g. how it's done on Heroku

Non-refactorings

Most or all of these will become individual issues / PRs. Just capturing them here for convenience now. Not all may make sense.

Deprecate existing get* endpoints (e.g. /getAllMarketPrices) in favor of '/exchange-rates', '/fee-estimate;
Eliminate dependency on bisq-core (only real need now is CurrencyUtil for list of supported coins)
Remove command line args for fee estimation params; hard-code these values and update them via commits, not via one-off changes by each operator
Remove 'getParams' in favor of Boot actuator endpoint
Update bisq-network/exchange to refer to 'provider' as 'pricenode'
Invert the dependency arrangement. Move 'ProviderRepository' et al from bisq-network/exchange here into bisq-network/pricenode and have bisq-network/exchange depend on it as a client lib
Save bandwidth and be idiomatic by not pretty-printing json returned from /getAllMarketPrices et al