prevent decompression DoS issues

[totaam]

Both the lz4 and zlib compressors now prevent decompressing packets that would consume too much memory: 83c72ba.
The default value is 256MB, which is enough for 8K in 32-bit BGRA format: 768043204 is ~128MB.

Unfortunately:

• lzo doesn't have the ability to limit its output size - perhaps it should be retired? (lz4 does everything better)
• brotli doesn't expose this ability through the python wrapper? https://github.com/google/brotli/blob/master/python/brotli.py

[totaam]

Also removed lzo from:

• Xpra-org/gtk-osx-build@e20a049
• Xpra-org/xpra-html5@da4093f

[totaam]

As for brotli, those concerned about memory bombs can disable it until we implement #3258.