teamspeak2 plugin: Code cleanup.

teamspeak2 plugin: Code cleanup.

The changes include:
- Use the ``tss2_'' prefix for all functions.
- Manage the global connection in two central functions rather than distribute
  connection handling all over the place.
- Handle ``global'' and ``per server'' statistics in one function.
- Using `getaddrinfo' rather than `inet_addr' to allow for IPv6 connections.
- Some formatting.