Build an iterative development environment

[stefanv]

At the moment, to get a local version of Fritz running all docker containers need to be built, including the SkyPortal one.

Consider putting in place Docker containers that mount the local filesystem, and then have a lightweight build update command to patch SkyPortal into the correct folder, after which fritz can be reloaded without rebuilding/restarting containers.

In short: we need to be able to rapidly iterate on code in Fritz as we do on SkyPortal, without costly build steps.