Auto mode for lossy compression

[joppuyo]

Add auto mode where both lossy and lossless compression are tried and the smallest file is chosen. This should be the default for JPEG files.

[joppuyo]

We could try to first encode image both in vardct and modular in the fastest speed, compare them, select the smaller method and encoding the final image with user selected speed.

We need to test if 1. this is actually faster 2. fast and slow encoding agree on which is the smaller.