Allow Viewing Local Layer Catalogs

[arottersman]

Often layers are completed on a small scale locally before creating the full set on s3. It'd be helpful to be able to verify these local layers before taking the next step.

[rajadain]

Add /data/input/ directory in the root of the repo, that gets loaded as a volume into the API container. Add instructions to the user in the UI and in the README that if they copy anything into this folder, it can be read from Trelliscope.

Add front-end options to list layers found locally, and the ability to select them.