Unauthorized MSA tree opening

Scenario 1

1. Open an alignment
2. Build the tree
3. Unload both documents (alignment and tree)
4. Delete the tree document from project
5. Load alignment
   Current state: tree document is added to the project, both documents are loaded.
   Expected state: only alignment is opened.

Scenario 2

1. Open alignment
2. Build the tree
   Current state: tree and alignment are both in the project, loaded and visualized.
3. Save the file and the project, relaunch UGENE
4. Open project, open alignment
   Current state: tree and alignment are both in the project, loaded and visualized.
5. Delete the tree document from the project
6. Save the alignment
7. Save the project
8. Relaunch UGENE
9. Open the project
10. Load the alignment
    Current state: tree document is added to the project, both documents are loaded.
    Expected state: only alignment is loaded.