BS-920
Disable validate action if no diagram active

Conflicts:
	bundles/plugins/org.bonitasoft.studio.validation/META-INF/MANIFEST.MF

Conflicts:
	bundles/plugins/org.bonitasoft.studio.validation/META-INF/MANIFEST.MF
	bundles/plugins/org.bonitasoft.studio.validation/src/org/bonitasoft/studio/validation/Activator.java
	bundles/plugins/org.bonitasoft.studio.validation/src/org/bonitasoft/studio/validation/BatchValidationOperation.java
	bundles/plugins/org.bonitasoft.studio.validation/src/org/bonitasoft/studio/validation/TokenDispatcher.java
	bundles/plugins/org.bonitasoft.studio.validation/src/org/bonitasoft/studio/validation/constraints/process/MessageEventConstraint.java