Vision should have tabs for quickly switching between queries

[mariusGundersen]

The vision tool is useful, but it's annoying that it can only save one query at a time. I'm forced to comment out queries as I test different things. It would be very useful to have multiple queries saved in local storage with a quick way to switch between them.

I propose we add a list of tabs above the main split panel, so that users can switch between different views. The tab panel would need a magic + tab at the end for adding a new tab. The title in the tab should be the first line of the query, excluding initial // characters, so that users can easily name the query by putting at comment at the top of the query.

Each tab would have a separate query and param, and maybe even perspective and dataset (so that changing the perspective only changes it for that tab, not the others). This means the localstorage object needs to support multiple queries/params/perspectives. Either the localstorage object is expanded to support this, or each tab controls a separate localstorage item, using an identifier that is appended to the namespace.