BS-7208 Fix choice of group iterator in Forms properties fields

Only possible to select/use in groovy script a group iterator in
- Initial value of widgets in a Group
- Show immediatly condition in contingencies
+ remove unused code
BS-7901 Refactor Group Iterator

- Add class GroupIterator
- Add initialization of groupIterator in existing/new group
- Set className of iterator to Object
- Changes on the Studio UI
-- add validation on iterator name and remove the one on className
-- add iterator in Initial Value expression viewer for widgets in Group
-- Group in Form should not havea access to iterator and Group in Group should have access => does not work yet.

- Add Migration on GroupIterator
Merge branch 'MasterBugFixing' into BS-7901_GroupIteratorExport
BS-7901 && BS-6926 Group Iterator export and correct availability in properties

- Add referenced groupiterator in the forms.xml
- Change availability in properties
- Change the representation of group iterator in available variables in groovy script editor
Merge branch 'MasterBugFixing' into BS-7901_GroupIteratorExport

Conflicts:
	bundles/plugins/org.bonitasoft.studio-models/form/form.gmfgen
	bundles/plugins/org.bonitasoft.studio-models/form/form.gmfmap
	bundles/plugins/org.bonitasoft.studio.common/src/org/bonitasoft/studio/common/ModelVersion.java
	bundles/plugins/org.bonitasoft.studio.common/src/org/bonitasoft/studio/common/emf/tools/ModelHelper.java
	bundles/plugins/org.bonitasoft.studio.console.libs/META-INF/MANIFEST.MF
	bundles/plugins/org.bonitasoft.studio.diagram.form.properties/src/org/bonitasoft/studio/properties/form/sections/options/contributions/InjectWidgetContribution.java
	bundles/plugins/org.bonitasoft.studio.engine/src/org/bonitasoft/studio/engine/export/EngineExpressionUtil.java
BS-7901 & BS-6926

- add changes in gmfmap and regenerated gmfgen to initialize the GroupIterator with empty name when created
- Ra-add case of groupiterator in EngineExpressionUtil and set correct type to output for the form.xml exported file
- Correct default validation of the GroupIterator name : the name can be empty if the iterator is not used in the Group
- Fix a validation interface (when validation of a name that is empty, it shows the name of the parent)
Merge branch 'MasterBugFixing' into BS-7901_GroupIteratorExport
BS-7981 Fix a previous merge (by hand ?)
Merge branch 'BS-7901_GroupIteratorExport' into 'MasterBugFixing'