Split off API and the editor into separate repositories

[jna-unikent]

As discussed previously, it would be great to split off the editor and the API into separate repositories.

Why?

• Removed temptation to closely couple them
• One or another could be swapped out independently of the other

[jna-unikent]

Lets have a planning meeting next week to plan this out.

[samyapp]

WIP / POC for this at https://github.com/unikent/astro/tree/sam/api-package.

Separating the editor out is quite straightforward, mostly involves updating some paths in webpack and gulpfile, but probably also needs some environment variables being set see #143 to avoid hard-coding things like the build path.

The API is more hard work - although this may be partly due to me not being that familiar with Laravel's internals yet. Still outstanding:

• assets
• config
• exceptions
• providers