polish & clean code (#566)

* Fix acq min bug

* Update docs, make `random_state` not a property of acqs

* fix giving bad seeds to l-bfgs-b

* remove debug code

* Relax constraint.approx test slightly

* GPHedge: ensure random state

* nitpick fixes

* Make constraints work with parameter types

* Use `deepcopy` when copying constraint in `ConstantLiar`

* Move the instantiation of `ConstraintModel`

* Update warning

* remove unnecessary random state storing

* Remove unnecessary import

* Add a `.random_sample` function to the optimizer

Author: till-m