Reduce the total startup time of the application and maintain sufficient responsiveness of the UI during startup due to the following:
1. Load resume data from disk asynchronously in separate thread;
2. Split handling of loaded resume data in chunks;
3. Reduce the number of emitting signals.
PR #16840.
Implement ResumeDataStorage class as base for all "resume data" storages.
Implement BencodeResumeDataStorage class and put all existing logic of
"resume data" loading/saving there.
