Refine operators and their parameters in TPOT

[weixuanfu]

What does this PR do?

1. removes the whole operators folder and replace it by using two python dictionaries (config_classifier.py and config_regessor.py) and a operator utils (operator_utils.py)

2. provides a new parameter operator_dict (-operator for command line) to easily customize list of operators and their parameters in TPOT using a operator dictionary file formatted as config_classifier.py. For interactive mode, this parameter takes a python dictionary directly and for command-line mode, this parameter takes file instead.

3. Adds a _pre_test decorator to decorate pipeline generator, crossover operator and mutation operator to make sure the new pipeline is workable with a small simulated dataset

4. fix > 15 unit tests for the new dynamically created operator classes.

5. Rebase Refine operators and their parameters in TPOT #343 with the latest dev branch

6. Rework pbar for better pipeline count

7. Add documentation for the new parameter for in command-line mode and interactive mode

Where should the reviewer start?

The operator utils (operator_utils.py)

How should this PR be tested?

Any tpot examples

What are the relevant issues?

#252
#296

Questions:

May need refine selector and preprocessor's parameters in the dictionaries.

[coveralls]

Coverage decreased (-7.7%) to 77.725% when pulling 41045ec on weixuanfu2016:config_dict_rebase_dev into 14a8173 on rhiever:development.