Channel switch

[kripton]

Some fixes from @jsjb (Update deps, switch from node-opus to @discordjs/opus, fix buffer warnings) and add a new method to the client to be able to switch channels.

@Gielert : Feel free to cherry-pick only the last commit if you do not want to check the others. Would be nice though :)

Example how to switch channels:

client.on('ready', info => {
  console.log('Connected to Mumble server:', info);
  console.log('===== Channels: =====\n', client.channels);
  console.log('=====');

  // Find the correct channel and switch if found
  for (var [key, value] of client.channels) {
    console.log(key + " = ", value.name);
    if (value.name === 'MyBelovedChannel') {
      console.log('Switching :)');
      client.switchChannel(key);
    }
  }
});

[Gielert]

Looks good! Thanks for the PR :D