Validate set uniqueness

Purpose:

The system should validate set for uniqueness before saving, so that set hierarchy was correct and filtration wasn't broken.

User story statement:

As a system administrator,
I want system to forbid saving non-unique sets
so that sets hierarchy complies to OAI-PMH protocol and allows proper records filtering

Scenarios:

1. Scenario - Set uniqueness validation success

• Given user creates/edits the set
• When user tries to save a set
• And set name is unique within existing sets
• And result setSpec is unique within existing sets
• And all other set validation rules are in compliance
• Then set can be saved

2. Scenario - Set uniqueness validation error

• Given user creates/edits the set
• When user tries to save a set
• And set isn't unique within existing sets due to duplicating name or result setSpec
• Then display a message "Set name or setSpec isn't unique. Please, fill in unique set name or setSpec to save set." in call-out
• And page with all set changes isn't cleared, so that user can correct the name/setSpec and try to save again