Add `itz api start` to serve up commands

[nathanagood]

To enable easy integration with a UI (such as an ElectronJS UI), itz api start will expose access to HTTP that maps to all of the commands via an HTTP post and the path as the name of the command. For example:

itz reservation list

is

http://localhost:5000/itz/reservation/list

and responds with the same JSON as running the command.

[nathanagood]

This has been implemented.