Remove ProxyAgent from being included in Toolkit Lib by default

[mrgrain]

Toolkit Lib should not force users to take a dependency on Proxy Agent. Instead it should accept an Agent (Node http Agent type) where it makes sense. The CLI as an implementor of the toolkit lib can and should still ship with proxy agent.

This will be some sort of API that allows the user to provide or return a https.Agent instance. That instance should be used where ever it is needed.