Adds handshake and connection source handling

## What is this PR? 

Adds handshake support and allows agent connections to control the message source.

## How it works

- [x] Adds token parameter to the agent constructor options
- [x] Adds token parameter to Connection constructor options
- [x] Makes Connection handshake message match virgo-base-agent handshake message
- [x] Updates Heartbeat feature metadata to match aep expectation
- [x] Nit: updates virgo.js version to match npm published version
@songgao call made is to not change the meanings of `source` or `target` and instead add something like `source_feature` `target_feature`