Give the IndexedDB database a more descriptive name that shows where it came from

[gae123]

The framework uses an IndexDB browser database to store some metadata it needs. It currently names this database keyval-store. When I first run into this database in the browser developer tools I was wondering where it came from.

We should give it a name that shows where it came from.

Contrast the sw-appcache name with the firebase one:

[jeffposnick]

My inclination is to leave it as-is for now, as updating it will be a breaking change.

I'm going to leave this issue open, though, and the next time we need to make a breaking change for any other reason, we can piggy-back on that and include this change as well.