@bgdnc please review below and hopefully this explanation will end up in the docs.

Further reference:
https://github.com/uberVU/mozaic/blob/master/core/datasource/datasource.coffee#L108-L144

Utils.newDataChannels will parse the parameters in order to prepare a dict of values of this form:
```coffeescript
{
    channel_type: channel_initialization_parameters
}
```
and then passing them next to datasource.

The datasource is initializing a new channel. What initializing a new channel means? Simplified it's something like this:
- prepare the channel configuration (taken from conf/datasource.js and stored in datasource.metadata[channel_type] (1))
- fetch the data

(1) Datasource is used as a singleton.

In Utils.newDataChannels you are passing a `channel_type` (all channel types defined in conf/datasource.js) that returns a channel instance guid, whereas in `subscribed_channels` you are using a channel instance guid