Add logging settings in settings page

• Move migrations to more related files (unrelated)
• Sync SignalConfig to and from SettingsBridge during startup and shutdown
  • Requires re-opening config.yml after gui has exited
  • The same settings are stored in two places (and synced)
  • This is because of SignalConfig being in Arc and changing that to e.g. RwLock seems a hassle and a half
  • But hey, it works!
• Re-enable running QSettings path migration at startup

Missing/considered features:

• Log rotation
  • Likely needs to be done manually because of SimpleLog (or I'm doing something wrong)
• Timestamped log files
  • e.g. harbour-whisperfish_YYYYMMDD_HHMMSS.log
• Saving logs to e.g. ~/Documents/Whisperfish/ instead?