fix s3 prefix generation
Move static resources into /assets subfolder.

Remove the weird "/static/static" folder.
Move the Singularity UI to a special "/ui" resource.

This frees up the root resource to be used for other things.
Make root resource configurable.

Add a new flag in the ui section: redirectRootToUi: true / false

If true, accessing the root URI of Singularity will redirect to the UI. If false, no redirection will
happen (and whatever other resource is configured for / will kick in. By default this is 404 (not found).
fix errors found in review