Overall totals, error filtering and notice checking.

[rumpletweezer]

Hello. I recently introduced pa11y-dashboard to the company I work for, and we are all very impressed, and can see it making a very positive contribution.

I have some feature ideas I believe would be useful to us, and may well be useful to others. I am happy to contribute code, but - reading the guidelines - I am starting by introducing the ideas here for discussion first.

1. It would be useful to have a total number of errors/warnings/notices for all the items held by the databases, so overall progress to a11y for a collection of items could be tracked in the same way as progress on each item already is. This might tie in with another feature request I saw to allow grouping of items.
2. I would like to be able to filter items by error/warning/notice - so items most in need of work could be identified easily.
3. A way of identifying the most impactful potential change. If (for example) a change of colour balance on a button which appears on many items would instantly fix many issues, make it easy to isolate. The best way to do this is not currently clear to me!
4. Where notices advise double checking something - ie where it is not possible to programmatically identify if there is a problem or not - it would be desirable to be able to manually dismiss the notice, and have pa11y-dashboard store that.

I am new to open source contributing, so I may need more guidance - please feel free to put me right!

Thanks again for all your work on pa11y-dashboard! It's a really exciting project in a hugely important area.