Our relationship resolver no longer tries to install conflicting mods.

If the user asked for conflicting mods, an `InconsistentKraken` is thrown.  

If mods we're installing or depend upon conflict with recommended or suggested mods, then the lesser mods are removed from consideration.

I'm a terrible person for not having huge numbers of test cases here, but I've been tested on huge amounts of CKAN metadata and discovering *all* my inconsistencies, so I'm pretty sure this works better than before.  :)

Example test:

    ./ckan.exe install CustomBiomes-Data-RSS CustomBiomes-Data-Stock

Includes #263, but happy to re-base if that gets merged and we want an easier to read PR.