* Add capability to train scale-variant MMOD models

* Review fixes: change bool scale_invariant to strongly typed enum, etc

* Add serialization and deserialization of assumed_input_layer_type

* Fix code formatting

* Rename things as per review feedback

* Review fix: move enum use_image_pyramid outside mmod_options

* Continue execution with net, if deserialization of shape predictor fails

* Revert "Continue execution with net, if deserialization of shape predictor fails"

This reverts commit 8ea4482c043b5b98b97ed5b78bfc6916a1e2a453.