Add a possibility to set service offering classes in config

[elenaustyugova]

Add a possibility to set classes of service offerings in config (UIDs).
Сlass defines the purpose of VM.

Acceptance criteria:

1. All SOs can be separated in these classes. As a result, there should be a grouped displaying of SO list (Change chooser components #293) - e.g. a class "high CPU performance" etc. One SO can be in different classes at the same time.
2. Each class should have a localized description
3. When changing a service offering (VM details) there should be only service offerings from this zone (connected to Offering Compatibility Policy Enforcing #567)
4. SOs with no class can be put in a class e.g. "common" (общий)
5. All SO classes and its descriptions should be localized

Connected feature ID: vm_creation_so