Operator: LA support: enhance LicensePlan editor with agreements management

[eparovyshnaya]

LiecnsePlan references a set of Agreements to be embodied into a license pack issued. The reference contains Agreements identifiers to be resolved in agreements domain.

Please extend LicPlan editor with the LicPlan::agreements reference editor.

---

Version: 2.0.1
Ported from bugs.eclipse.org: 575433
Ported fromEclipse Passage Issue 955