(DNN-4598) Can't edit extensions when "AUM_ForceLowerCase" is true

KEYFIELD was not getting replaced by {0} if AUM_ForceLowerCase was set to True in the HostSettings table because it was uppercase in the code and lowercase in the actual url.
Revert unintended changes
Merge pull request #51 from bdukes/DNN-4598

DNN-4598 Can't edit extensions when "AUM_ForceLowerCase" is true