* gym.spaces.Dict inherits from collections.abc.Mapping
It would be very convenient to have `gym.spaces.Dict` inheriting from `collections.abc.Mapping` so that it can be used in conjunction with [dmtree](https://github.com/deepmind/tree) to perform operations on complex spaces conveniently. It also simplifies the implementation which is good.
I just don't like the fact that the `contains` method behavior is not consistent with what it should be doing if it was a proper mapping...
* Update dict.py
* Update dict.py
* Make the seed in default initialization controllable
Since seed() is being called in default initialization of Space, it should be controllable for reproducibility.
* Updated derived classes of Space to have their seeds controllable at initialization.
* Allow Tuple's spaces to each have their own seed
* Added dict based seeding for Dict space; test cases for Tuple and Dict seeding
* Update discrete.py
* Update test_spaces.py
* Add seed to __init__()
* blacked
* Fix black
* Fix failing tests
* Fix seed method for Tuple and Dict
* Improve stochasticity
* Update test cases for seed method
* Update test cases for seed method
Update test cases for seed method
Update test cases for seed method
