refactor: prepare the code for thread replies

This MR includes several refactorings that are loosely finishing the first two tasks from #339 (closed):

1. Enable responses
2. Extend the createNote method to return notes (with positions), instead of void

This MR doesn't have any user-facing effects except for better logging of error that might occur when we create a new note.

The refactorings in this MR have two goals:

• fetch createNote permissions and use them to decide whether the user can respond to a thread
• when creating a note, fetch the newly created note from the API (up until now we were only interested in whether the mutation succeeded)

This MR is best-reviewed commit-by-commit. Detailed explanation for the changes is in commit messages.

Related to #339 (closed)