Add visible sync status for be_groups records

[christianfutterlieb]

Add a new functionality to calculate the sync status of a be_groups record.

The sync status can be one of:

Status	Description
not-synced	The be_groups record has no role definition
out-of-sync	The be_groups record does not have the same definitions as its assigned role
sync-ok	The be_groups record has the same definitions as its assigned role

The status is made visible as iconOverlay of the be_groups icon. Note: integrate with existing overlays (hidden, starttime, endtime, ?). If it does not integrate well enough (say: interferes too much with the existing TYPO3 icon/overlays), it will just displayed it in the overview list of the Backend Module