Revamp build coverage page

[williamjallen]

This PR completely revamps viewCoverage.php, one of only two remaining pages using XSLT. This change builds on significant work over the course of the last few months to expose the necessary data via GraphQL. The previous XSLT-based page had numerous issues which are resolved by this PR.

After:

Before:

[josephsnyder]

I like the revamp. Filtering seems complete ( Though I don't have function or branch coverage to test).

My only request is this:

Can we make more obvious the way to get "back" from nested directories?
The current page framework does load a "new" page on click so using the Back button is how you'd get from test/src/a to test/src. The current page lets you click into the subdirectory without updating URL parameters which means the Back button might take you to the Project page instead of the higher level directory.

Maybe an "Up" icon or link that appears next to these breadcrumbs when you are in a non-top level directory?

[williamjallen]

@josephsnyder What about a "back" button like this as a shortcut to the previous directory? It's worth noting that the breadcrumbs themselves are (supposed to be) clickable. While testing this some more, I found a bug with the breadcrumb navigation and I'll push a fix shortly.

[josephsnyder]

I like that back button a lot. I wish that it could be disabled or disappear when the top level is reached, but I'll happily approve what we have.

[williamjallen]

@josephsnyder Ah, good call. I'll disable the button at the top level.

[josephsnyder]

No other comments. LGTM!