SimpleWorkflow service message validation - EUCA-9812

SimpleWorkflow request messages are now validated and a ValidationError
response is now returned for invalid messages.

EUCA-9812
SimpleWorkflow service support for quotas and limits - EUCA-9624

Quotas are now supported for domains:

 * swf:quota-domainnumber

and limits are added for other swf resources with default values as per
AWS/SWF.

EUCA-9624
Merge remote-tracking branch 'origin/dev/sjones/EUCA-9624' into testing