• More robust TDM file reading attempts: we now try until we can access them or until a 5 second timeout
• If a TDM file is not found at all, we now continue immediately and don't wait the 5 seconds
• Rework auto-refresh system to be simpler and more robust:
  • Refreshes run completely on the UI thread now
  • Refreshes happen immediately or not at all; no more deferred refreshes
  • Refreshes are not allowed when the main window is blocked or disabled (mostly if a progress box is up)
  • If a dialog window is open (Settings, About, etc.) then a "lightweight" refresh (UI update only) is allowed, but a "heavyweight" refresh (FM list reload, possible scan and/or readme cache update) is not.
• Remove installed status from unavailable TDM FMs (those not found on disk)
• Gracefully handle scenarios where some or all watched TDM files or directories may not exist (clean install, partially broken install etc.)
• Ignore empty or invalid FM dirs (dirs with no pk4 files in them; TDM clean installs may add an empty "saintlucia" folder for example)