Split sub-recipes

[a-type]

Allow splitting a portion of a recipe into a sub-recipe. This is done in a modal which lets you checkmark-select the ingredients and steps to move. Once complete, the sub-recipe is embedded into the original, with a section in ingredients and a movable step that links to the sub-recipe and can be expanded to show its steps together inline.

When editing a recipe, you can also embed another recipe in the steps editor by selecting "link another recipe" which appears in a blank step line. This adds the embedded step and automatically embeds ingredients.