Improve performance of errata checking in ETT and fix fanthom nvr in errata

Remove N+1 errors

Sometimes an nvr is removed in the errata but ETT still thinks it's in the
errata. This commit also fixes that logic so that it correctly flags an nvr as
in errata or not.
Merge pull request #139 from thescouser89/nvr_in_errata_fix

Improve performance of errata checking in ETT and fix fanthom nvr in errata
Change empty to nil
Merge pull request #140 from thescouser89/nvr_in_errata_fix

Change empty to nil
Fix for the previous commits
Merge pull request #141 from thescouser89/nvr_in_errata_fix

Fix for the previous commits
Add hyperlinks to brew and mead fields

Thanks Tom for the suggestion!
Merge pull request #142 from thescouser89/hyperlink_brew_link

Add hyperlinks to brew and mead fields