Iron some inconsistent names in the web UI

[reydelamirienda]

In some of the status pages, misleading terms are used that confuse users with no knowledge of Nix and Hydra, and even those who know about how it works internally.

For example:

• /project/{project}: The column 'Last evaluated' is actually displaying 'Last checked' as it is shown under /jobset/{project}/{jobset}. This should be fixed to avoid confusion. Either display last checked with the proper heading, or display the 'Last evaluation' value since it's more meaningful.
• /eval/{eval}: The column 'Finished at' for queued jobs makes no sense to me. It simply shows the current date, when it should show nothing.