Add !whykarmadown !whykarmaup commands to mod_karma

[Roobarb]

Users should be able to give a reason to a karmaup/karmadown action using a hash sign, for example:
!something++ #because of reasons
Which would increase the karma of 'something' and store 'because of reasons' as a reason for this karmaup action.

Requires a new table 'whykarma' with fields karmaitem,up/down,reason and a rewrite of mod_karma

When this is done we can import whykarma.csv from unox