Fix app freezing when creating toast messages

[thePeras]

Closes #727

Basically, there was a problem with contexts.
When creating a new reference, the created dialog was initializing a new isolated context. That context was being passed to the toast and used it to close the message after a period of time. However, the dialog was already closed when the toast tried to close itself, and it wasn't being able to do it.

Review checklist

• Terms and conditions reflect the current change
• Contains enough appropriate tests
• If aimed at production, writes a new summary in whatsnew/whatsnew-pt-PT
• Properly adds an entry in changelog.md with the change
• If PR includes UI updates/additions, its description has screenshots
• Behavior is as expected
• Clean, well-structured code