Warn on live ebuild with older EAPI than release

[thesamesam]

If we have:

• x-1.ebuild with EAPI=8
• x-9999.ebuild with EAPI=7

then this implies the live ebuild is unmaintained and should be removed (or fixed, obviously, but probably removed).

We can do this either by checking for PROPERTIES="live" or we can do this based on version comparisons (which would include non-live ebuilds too). I fear the latter is too vulnerable to false positives where software has multiple branches, so let's do the PROPERTIES inspection instead.

i.e. Take the max of non-PROPERTIES="live" ebuilds for a package and take the min of all PROPERTIES="live" ebuilds for a package. If max_non_live_eapi > min_live_eapi, warn.