Implement custom grouping of test cases

[fkryvyts-codete]

Currently there is no way to group multiple test cases. Purpose of this task is to introduce such functionality.
The idea is to create new mechanism of folders or groups that can include multiple test cases. Ideally user can via drag-and-drop create hierarchy of such groups (folders) by nesting them inside each other. Each group will have its name defined by user. If any test case or sub-group inside such group fails then all group will have status "Failed".
Chances that need to be done are following:

• Modify server's code and add endpoints for test groups management
• Create new page for GUI application that will allow user to create test groups hierarchy and another page that will allow user to track current status of each test group.