Thumbs: render all holders directly with proper dimensions
Renamed update_browser to select_in_browser, added support for selecting folders initially
Removed complex orientation-related optimization, now we always read metadata before showing the image
Fix: when loading a large new folder, thumbnails were delayed till very end of holders-loading or till user scrolled. Now they start loading immediately.
Browse: clear pending add_image timeouts when changing folders
More manageable cache: put filename in cache thumbnail paths
Initial browse history support