merged
use PromotionsContextHelper in subpackage promotions
Merge remote-tracking branch 'origin/promotions' into promotions

Conflicts:
	job-dsl-core/src/main/groovy/javaposse/jobdsl/dsl/helpers/PromotionsContextHelper.groovy
	job-dsl-core/src/main/groovy/javaposse/jobdsl/dsl/helpers/promotions/PromotionsContext.groovy
	job-dsl-core/src/main/groovy/javaposse/jobdsl/dsl/helpers/promotions/PromotionsContextHelper.groovy
	job-dsl-core/src/test/groovy/javaposse/jobdsl/dsl/helpers/PromotionsHelperSpec.groovy