Use Recipe Object, not string, as main state

[ascibisz]

For our "source of truth" for the current state of the recipe, we should have a Recipe Object, rather than a string

[meganrm]

• 1. store recipeId and recipeDisplayName (could be one object with two fields)
• 2. store only user changes and then write a selector that overwrites recipe defaults with the changes
• 3. derive "isModified" by having an non-empty userChanges object
• 4. rename things with "input": ideas "userSelections" and "editableRecipeFields"

[meganrm]

I took care of #1 in #132