Snapshot support

Currently we only support the last minor version of Minecraft (1.7.10, 1.9.4, ...).

We could check in every version check for the snapshot protocol version to handle changes. This would mean, we would get rid of the enum ProtocolVersion and from the Protocol_x_x_x files. To get a list of available protocol versions, we could just load a json (like in the flattening updates) and parse them. The other solution would be to allow all versions.

There are still several problems:

• What about the mapping folder (assets/mapping)?
• Is this necessary?

ToDo:

• Flattening: All packets (like the EntityMetaData flattening update in f692d131)
• ...