This change fixes two issues with Modelfiles:
1. If a user uses `ollama show --modelfile` to show a safetensors based
model, the Model would leave the "FROM" field blank which won't allow
a user to recreate the model. This change adds the model's current
canonical short name to the FROM field.
2. If a user uses the `/save` command in the CLI any messages which were
saved in a previous model wouldn't get saved (only the set of messages
from the current session).