Make Pipeliner use any grid object with sklearn structure

[lodurality]

As of now, Reskit has a hard coded GridSearchCV as a default grid object. We need to do the following:

0. Add parameter grid_object which specifies grid object. Right now in the code, we have grid_clf.

1. Pipeliner should work for testing single models without grid search (grid_object = None). If grid_object = None then Pipeliner doesn't use param_grid and makes cross_val_score on pipelines with params specified in steps.

2. If we specify grid object then we should have grid_object_params (default None) for non-classifier specific grid search parameters. For example we can specify in grid_object_params n_iters for RandomizedSearchCV. Setting of all grid_object parameters should look something like this grid_object.set_params(**self.grid_objects_params, param_grid=self.param_grid)