Allow users to declare their own port

[ayyrickay]

The Dev Phone should have a --port flag that allows them to easily declare their own port. Additionally, the dev phone should have a stronger stance on which ports it uses and how those relate to standard ports used in web development.

This feels like a necessary first step for #24 and also a part of #110. We need to understand what port we're using (and potentially persist it) to handle multitenancy on a single machine, which eventually may scale to multiple machines working on the same account.

[ayyrickay]

Potential spin-off of this issue or an improvement to this PR: https://www.npmjs.com/package/get-port