[ENH] Separate Pretty Printing from sklearn dependency

[RNKuhns]

Is your feature request related to a problem? Please describe.
A clear and concise description of what the problem is.

Eventually the baseobject package will not depend on scikit-learn's BaseEstimator. This will be accomplished by gradually removing the BaseObject dependencies on BaseEstimator for different API interfaces and features.

This issue covers the features that need to be added to BaseObject to remove the dependency on BaseEstimator when pretty printing instances of classes that inherit from BaseObject.

Describe the solution you'd like
A clear and concise description of what you want to happen, ideally taking into consideration the existing toolbox design, classes and methods.

BaseObject should contain all the functionality needed to implement the pretty printing. However, we need to investigate and eventually decide the degree to which the functionality in BaseObject should identically recreate the pretty printing functionality present in BaseEstimator.

Important considerations are:

• Ease of maintence
  • There may be ways we can get a similar effect with less code to maintain, but we need to understand how the pros and cons associated with any different implementations of this functionality
• How BaseObject interacts with sklearn classes/pipelines when pretty printing representations of classes
• Need for adequate tests to ensure pretty printing is working correctly and meets the level of compatability with sklearn that we choose