Compress server_state.bin

Currently, my Stonehearth savegame directory has 1.65 GB, and the typical save has 25-50 MB each. The bulk of it is the file server_state.bin.

It would be nice, if Stonehearth savegames were somehow compressed. E.g. applying a gzip filter reduces the server_state.bin by a factor of 4-6, depending on the chosen performance/compression trade-off.