Voice prototype for 3.1

[quanticc]

Currently toying with some changes to voice module in 3.1:

• Create a voice gateway implementation that's more symmetric with normal gateway impl
• Add resume and automatic reconnect capabilities
• Move some classes to common module as they are used in gateway+voice.
• Allow customizing the send and receive task factories, UdpClient and schedulers
• Move the previous implementation under a FSM prefix
• Expose VoiceSendTask and VoiceReceiveTask for customization

Attempting to cover the following tickets: #536 #523

As this PR only takes care of translating the current impl to a more malleable pattern, only some of the items in #427 are to be covered:

• Implement reconnect and resume functionality for VoiceGatewayClient
• Restructure to allow for custom voice clients
• Add information to logger names to distinguish when multiple voice connections exist

Pending work (to be handled in separate PRs/commits to master)

• Handle multiple attempts to join the same channel
• Handle moving channels
• Add docs to new classes
• Example for standalone voice module usage
• Polish loggers and levels

And beyond the scope of this PR:

• Update migration wiki page
• Provide support/feature parity to the FSM implementation
• Provide mappings for ssrc -> user id for receive
• Explore options for converting completely to netty's ByteBuf

Since we only push snapshots on release and maintenance branches, testing this is only possible through jitpack.