WebServer: The filenames weren't correctly URL decoded.

Filenames with "special" characters were always leading to 404 errors.

This commit fixes #84.
Fix "Auto-fit" and "Auto-fit (Larger Only)" zooms in fullcreen mode.

"Auto-fit" and "Auto-fit (Larger Only)" zooms were giving different results depending on if they were used in windowed or fullscreened mode.

This commit fixes #2881.