Add feature for defining model specifications

[duranb]

resolves #1212

To test:

1. Create constraint(s)
2. Create scheduling condition(s)
3. Create scheduling goal(s)
4. Create a model
5. Click on the newly created model in the models table
6. Click on the new "Edit details and associations" button on the left, under the model's metadata
7. Verify that you are taken to the new edit model page
8. Modify the model metadata (i.e. name, description, etc)
9. Click on the "Constraints" tab
10. Click the "Library" tab
11. Toggle on the checkboxes for all the constraints that you want to add
12. Click the "Model" tab
13. Verify that all the constraints that you toggled on are present
14. Choose specific versions of the constraints that you prefer
15. Click on the "Conditions" tab and repeat steps 10 - 14, but for scheduling conditions
16. Click on the "Goals" tab and repeat steps 10 - 14, but for scheduling goals
17. For goals, also update the priority if desired
18. Click the "Save" button at the top right
19. Verify that all changes are persisted after a refresh