First crack at auto-thumbnail generation, and a bit more default style to display them semi-nicely
Leave media_folder var at generic default (whoops); catch and avoid another crash when trying to list a subdirectory without read perms
Give subdir read error a more accurate status code (403 vs 404)
Add media subdirectory to .gitignore; URLencode filenames for use as f GET param, fixes crashes related to special chars in filenames