Generate ConditionElements in aws.py instead of manipulating globals

[michael-k]

I think the code for the ConditionElements in awacs/aws.py should be generated instead of manipulating globals.

The current implementation makes it impossible for static code checkers (linters, type checkers, …) to handle it correctly. Eg. pylint reports a no-name-in-module error for from awacs.aws import StringEquals.