Use magix affix group during item generation

[mofr]

Otherwise, an item can have both affixes in the same group and something like Fox and Mammoth so +31 to Life and +11 to Life. Those affixes are mutually exclusive because they are in the same group when you pick the first one that discards all other affixes from that group.
Using of the Fox suffix, for example, is in group 26 and will discard 41 other affixes that are in that group.
Also, a given group ID is shared by prefixes and suffixes, so if you take a prefix in group 26, you also discard all suffixes in group 26.

cc @giviz