Parse evaluation warnings and display in separate section.

[MagicRB]

A live version can be seen here and in case my buildbot dies or gets reset, a screenshot:

Possibly fixes #172, for anything more fancy we'll need #173, what do you think @zimbatm?

And due to the exploration here, I've learned that we can add arbitrary HTML to the page, as long as it is contained in one of those tabs. Well, injecting javascript and modifying the page is an option, but a really bad one :)

[MagicRB]

Anything more than this is blocked by #173 and further discussion is needed, as buildbot does not allow partial UI replacements as far as I can tell, therefore we cannot add another element into the build UI.

[zimbatm]

Unless the eval error gets more visibility, it makes sense to table this for now.

[Mic92]

@mergify rebase

[mergify[bot]]

rebase

✅ Branch has been successfully rebased

[MagicRB]

This is superseded by #255 as now evaluation failures appear as separate builds.

[Mic92]

But is this the same as warnings though?

[Mic92]

But is this the same as warnings though? Those

[MagicRB]

Ah yeah if the build doesn't fail it doesn't show. That's my mistake.

[Mic92]

Fixed: https://github.com/nix-community/buildbot-nix/pull/485