refactor files

[xuanfeiren]

Move the PS search family from features to the main code and retire the other trainer implementation as examples.

[chinganc]

@xuanfeiren Thanks for initiating this. Here're some changes needed still. Thanks.

• Move things opto/trainer/supporting_files back to opto/trainer/ except for the following.
• Move opto/trainer/supporting_files/examples.py' opto/trainer/algorithms/classical_algorithms.py`
• Where is `opto/trainer/supporting_files/module_regressor.py' used? if not, remove it.
• Move opto/trainer/examples to examples/trainers and remove aggregator.py there, as we discussed.

[chinganc]

LGTM. @allenanie Can you run some tests on the trace bench with this PR? to make nothing is broken there. If not, I think it's ready to be merged.

[chinganc]

Integration with trace bench was tested. It is found PS misses the mechanism of selecting the best candidates via validation. Fix to PS will be implemented in future PR @xuanfeiren @allenanie .