Possible partial fix for #952, #1235, #1343

[wcole3]

Initial attempt to fix xyz_grid script loading checkpoints. Tried using the onchange in modules/initialize_util but got some odd lockups probably developer error.

This should minimize the reloading during a x/y/z grid run, but it does result in the first non-script run after running the xyz-grid to reload the model.

VAE changing between run still wip.

Ref issues: #952 #1235 #1343

[lllyasviel]

My concern is that the name refresh_loading_params is too formal and looks like main entry for that functionality when it is not maybe refresh_loading_params_for_xyz_grid or similar is a better name. also maybe this func can be moved to xyz_grid file as they only serve xyz

[wcole3]

Makes sense to me, refactored.