Rework into multiple jupyterlab extensions

[SimonBiggs]

Make each component be its own JupyterLab extension.

https://gitter.im/jupyterlab/jupyterlab?at=5b65c83d945df30dc152a618

Then install all those extensions, and load them up in the same way that jupyterlab loads up its own extensions.

That way the scriptedforms components might also be able to be used within a notebook.

But primarily it will be a good framework for users to add their own components to ScriptedForms.

[SimonBiggs]

Make it so the component selector only works if it is a sub child of a top level scriptedform element. That scriptedform element must contain within it a reference to what kernel it is using. That way the scriptedform elements do not run globally within JupyterLab and whenever they do run, they know what kernel to use.

Should a scriptedform top level component be created within a notebook then it could default to using the kernel that the notebook is using.