Sync misc changes (#673)

* allow state info in filename of saved images from imaging callbacks

* Fix test

* Fix test

* fixes to schedulers with backward compat

* fixes to schedulers with backward compat - remove extraneous epoch param

* remove debugging

* add additional tests and fixes

* Update torchbearer/callbacks/torch_scheduler.py

* Fix tests

* Clean up tests

* Fix torch scheduler last epoch argument

* Add warning when resuming with step_on_batch=True

* Remove last_epoch argument from scheduler callbacks, clean up tests

* only step when training

* update tests now that model is expected to be in state

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Co-authored-by: Ethan Harris <ewah1g13@soton.ac.uk>