Refactor optimizers

Update the way optimizers are handled

Previously optimizers needed to inherit from our base class BaseOptimizer. In this version users can more easily pass in their own optimizers, which are then wrapped in a custom class performing some postprocessing steps. As a result of this change, we have removed the LASSO and ElasticNet optimizers since their corresponding sklearn objects can now be passed into the SINDy object directly.

Minor changes

• Added quiet mode to SINDy.fit
• Use L2 regularization by default for STLSQ