ENH: Add LinearSVR

Fix #1473
remove class_weight parameter
fix random_seed in test
format cleaning and comment for different parameter name
remove unnecessary ravel
update docstring for hinge_loss
hide epsilon and svr in LinearSVC
Revert "update docstring for hinge_loss"

This reverts commit f7ef3b910a4d59443d228dfa9fb55a5f83a641d6.
test against original liblinear
REFACTOR liblinear based estimators

BaseLibLinear -> LibLinearMixin
comment for parameters not shared by all
LibLinearMixin should inherit from object
solver_type check for liblinear based estimators

1. solver_type check is done only in fit
2. more informative error message
3. add test for parameter combinations for LinearSVR
4. clean parameter combination test for LinearSVC and LogisticRegression
mv _solver_type_dict to subclass

Before this, you can set loss = "lr", "l1r", "lr2" in LinearSVC to do
logistic regression and linear svr.
clean preparation for fitting

1. combine _transfrom_data and _validate_data to _prepare_fit
2. rely on self.class_weight_ for class weight
fix shape of LinearSVR prediction
Add blank lines