[Bug] Potential temporary memory leak when a webpage inserts and removes lots of frames

[jspenguin2017]

1. When the main frame is navigated, its frames are not cleared from tab store.
2. When a frame is removed, it is not reflected in the tab store.

The first problem is easy to fix, but it's not that important, maybe 1 kB here and there, no rush for that.
The second problem is more difficult to fix, it affects uBlock Origin (and Nano) as well.

[jspenguin2017]

1 is fixed. I'm not sure how to deal with 2 though...

[jspenguin2017]

gorhill/uBlock@feabfe3