Feature Request: Ability to use multiple discrete instances of PW-Core simultaneously.

[jordanmack]

• I'm submitting a ...
  [ ] bug report
  [X] feature request
  [ ] question about the decisions made in the repository
  [ ] question about how to use this project

• Summary
  It would be beneficial to be able to have multiple instances of PW-Core that are simultaneously initialized to different chains or with different configurations.

When building dapps that use both the mainnet and testnet, the developer is forced to continuously reinitialize PW-Core each time the focus is switched to a different network. There is no way to initialize once and store instances that can be reused as needed.

The internal use of singletons provides some simplification of structure, but this adds significant complexity to work around this limitation for any dapp that needs to work with multiple networks.