Horde AI + Preset setting improvements  #51

Describe the bug

1. Switching between menus, the Horde AI + Preset list will reset to default (still retaining the previous setting until they modified)
2. If Horde AI model becomes unavailable, the horde will send back that the generation is not available looping over and over giving no input to user.

Expected behavior
Update list button for horde model selection and retaining settings.
Feedback to user that the model and halting generation if it is unavailable.
Model priority list if one goes offline.