Show all loaded recordings as tabs

[emilk]

When you have loaded more than one recording, show them all as tabs instead of hiding them under the Rerun menu.

The current hiding of them makes it difficult to discover that there are many recordings open, and makes it difficult to switch between them to compare.

Having them all as tabs lets you quickly switch between and compare them, and we can even allow docking them to compare side-by-side.

[emilk]

This will also make testing easier. Right now run_all.py --separate spawn a lot of instances of rerun, which is very annoying and without --separate you get one rerun and no easy way to switch between the loaded instances.

[emilk]

Closing in favor of:

• Show open recordings in side view above blueprints #2298