Allow condenser to run against different chains (#1563)

* Add support for custom chains

Needed for condenser to fully work with testnet

* Don't use hardcoded address prefix in BrowserTests

* Remove memo encryption test from BrowserTests

A similar memo encryption tests are run somewhere in steem-js when memo.encode is called causing this to throw even if that wasn't the intention.

* Drop custom prefixes for chain id and address prefix config vars