[Enhancement] Allow clicking on domain to expand it to show hosts

[Gitoffthelawn]

Currently uBlock popup UI has an "All" expander to expand all domains to show the hosts.

Proposal: Allow clicking on any domain to only show the hosts for that domain.

[luxoflux]

That would be a nice quality-of-life enhancement.

[gwarser]

Can be closed?

[gorhill]

I want to give more thoughts on finer details:

• No need to expand when all subdomains are already visible (example, see https://news.ycombinator.com/)
• When a subdomain is cname'd but not the base domain, should the cname'd be always visible? (example, https://en.wikipedia.org/wiki/Main_Page)
• Whether there should be a widget on hover for toggling expand/collapse (example, like in uMatrix)

I haven't made a decision yet about these.