Ensure that on import, default style loads about yellowbrick

[bbengfort]

See #3 - Yellowbrick needs its own, default style and color palette; similar to Seaborn. This style needs to be loaded on init, so it cannot be:

1. destructive (e.g. it must look for resources, and if it doesn't exist, don't quit)
2. intensive (it must be lightweight and simple)

To that end we also want a number of ways to configure Yellowbrick:

1. From an environment variable, YELLOWBRICK_STYLE and YELLOWBRICK_CONTEXT
2. From a Jupyter configuration file
3. From something like Confire for YAML based configuration.

[pvomelveny]

Actually this answers my question I asked in Issue #3

Do we want to mimic Seaborn and try to have our style/palette objects/functions be basically compatible? How Seaborn-y do we want to be?

[bbengfort]

I'd certainly like set_style and set_context to work in a similar way (though they jump through a lot of hoops as far as I can tell) but I'd also like us to have our own style based on Color Brewer. In terms of compatibility, was there anything specific you were thinking of?