Update Indicator bindings only to output the negate attribute if it is not None or False. Update the Indicator API to default negate to None, and to allow get/set of negate. Setting the negate value to anything other than 1, '1', or True will cause the object to set negate=None
Change setter to use None instead of False
Fix bad default value
Merge pull request #180 from STIXProject/indicator_negate_fix

Update handling of Indicator's negate attribute