UI: list what network is monitored and provide option to switch

[BigLep]

Done Criteria

1. The dealbot landing page UI makes clear what network(s) are monitored (calibration or mainnet)
2. Provide an option to switch to view a different network.

Specifically, dealbot.filoz.org should list "mainnet" and have a way to select "calibration", which "redirects" to "staging.dealbot.filoz.org" (and vice versa).

Why Important

Make it more self-service to make clear to understand what a particular dealbot instance is monitoring and how to switch.

Notes

1. We should do something cheap/scrappy here, as the real goal is to have a single instance be able to monitor multiple networks: a single dealbot should be able to talk to both mainnet & calibration #297