CMOS can't be run behind a path-based reverse proxy

Currently there are a lot of places where we're running on our own host/port. If you try to deploy CMOS behind a path reverse proxy (e.g. on bigstuff-industries.com/cmos rather than cmos.bigstuff-industries.com), various components break to the point of being unusable:

• Homepage redirects you to port 8080 even if it's being proxied on another port
• Grafana dashboards 404
• Add Cluster form cannot add a cluster (and might say it was added successfully when it really wasn't)