Refs #4468: Copy of 3.0 content
Fixes #4468: Add check box to enforce or not group content
Merge pull request #289 from VinceMacBuche/ust_4467/implem_4468/enforce_group_content

Fixes #4468: Add check box to enforce or not group content
Refs #4469 : clone 1.1 to 1.2
Fixes #4469: Add empty value variable and overridable variable support.

Make the variables overridable to prevent cfengine spouting warning
lines over variable redeclaration
Merge pull request #290 from VinceMacBuche/ust_3848_implem_4469/handle_empty_variables

Fixes #4469: Add empty value variable support.
Refs #4469: add changelog
Merge pull request #292 from VinceMacBuche/4468_changelog

Refs #4469: add changelog
Merge branch 'branches/rudder/2.6' into branches/rudder/2.8
Merge branch 'branches/rudder/2.8' into branches/rudder/2.9