Add uncertainty quantification methods (#816)

* * adding changes from linter. * squashing last few PR commits into one. * PR is still 1) uncertainty (auc) methods, 2) datagen refactoring, 3) minmax for functional particle VI.

* Fix some docstrings (#833)

* adding changes:
* adding test for eval_uncertainty
* removing some unused code for packages.
* created file sl_utils with loss functions and uncertainty related functions

* use random data instead of saving/loading mnist data for eval_uncertainty test, also incorporate changes from master

* * integrated alf configurable data_loaders
* fixed docstrings according to comments

Co-authored-by: emailweixu <emailweixu@gmail.com>