Review how the GUI is repainted to fix a crash

Problem

This scenario is reproductible for the "Active sessions" and "Monitoring" tabs.

• Start a session with one big file.
• Start a second session with a lot a small files.
• Pause the big upload.
• Cancel the big upload.
• While the confirmation is displayed, the crash happens.
• If not, wait a bit for a small transfer to finish.

The spot here is the confirmation popup being deleted while the items list ( either the sessions, either the transfers) is refreshed. The refreshing is removing all rows and inserting new ones. Thus the confirmation popup reference being freed and the crash.

Solution

Instead of refreshing all rows, we should just refresh pertinent and desired rows.