BS-1871
BBPMC-113 add validation on paralell gateway design

Conflicts:
	bundles/plugins/org.bonitasoft.studio.validation/messages.properties
	bundles/plugins/org.bonitasoft.studio.validation/plugin.xml
	bundles/plugins/org.bonitasoft.studio.validation/src/org/bonitasoft/studio/validation/i18n/Messages.java