added workflowhistory method, made getContextObject public so it is retrievable from workflow action controllers
added workflowhistory method, made getContextObject public so it is retrievable from workflow action controllers

icecaster/advancedworkflow,dnadesign/advancedworkflow,dnadesign/advancedworkflow,silverstripe-australia/silverstripe-advancedworkflow,icecaster/advancedworkflow,Internetrix/advancedworkflow,silverstripe-australia/advancedworkflow,silverstripe-terraformers/advancedworkflow,Internetrix/advancedworkflow,silverstripe-australia/silverstripe-advancedworkflow,silverstripe-terraformers/advancedworkflow,silverstripe-australia/advancedworkflow