Add support for REST requests to be triggered

[jamsidedown]

Is your feature request related to a problem? Please describe.
Currently all functionality is expected to be performed via websockets, however there are cases when a rest call may trigger a websocket response that needs to be tested.

Describe the solution you'd like
I want to be able to trigger rest requests to be sent when websocket responses are received. I would also like to be able to add triggers to the response from a rest request.

Describe alternatives you've considered
An alternative would be to have separate rest requests being made while a websocket test is running asynchronously.

Additional context
No additional context.

[jamsidedown]

The first version of rest requests has been added by #43
As we use this tool internally, new features should become apparent so this issue will be ongoing for a while I think.