Improvements and fixes

The device chart stays visible at brand-new plants, the sign-in page opens without an error, and you can search subnets for plant clashes.

• At a brand-new plant, the round device chart on the "Networking" page no longer disappears. Each device simply stays grey until its first readings arrive.
• The sign-in page no longer shows an error message when you open it or after you sign out.
• Search and filter the subnet list by portfolio and plant; subnets claimed by two plants come first, so clashes stand out.
• Your certificate now shows its public key and creation date, so you can check the configuration file you downloaded is current.
• On a phone, you now pick a page's tab from a dropdown instead of a tab strip that ran off the edge of the screen.