Add favorite recipes

[mueller-ma]

Is your feature request related to a problem? Please describe.
I'd like to mark some recipes as favorites, so I can access them faster. The favorite state should be synced.

Describe the solution you'd like

In several views add a "mark as favorite" option, e.g. in the recipe view add a button next to the share button. On the start page show a row of the favorite recipes, similar to what is done now with categories.

Additional context
<! -- Add any other context or screenshots about the feature request here. -->
Technically implement this by adding a tag to favorite recipes, e.g. the emoji ❤. This seems to a good multi-lingual approach to get the favorite state synced without changing the API.

At least on the web ui adding such a tag works fine:

[lneugebauer]

I like the idea to use a special keyword to sync a favourites state.

Before implementing it, I'd browse through the nextcloud cookbook repository to see if they plan to support this natively.

I think the recipe detail screen should get a button added to the top bar to toggle favourite state.
On the list screen, a swipe action should be added to add a recipe to favourites quickly.
The home screen shows the three categories with most recipes in it. Additionally, favourites should be added as a fourth one and placed after the recommendation, if there are any recipes marked as favourites.

It'd probably be a good idea to have the keyword to use for this be configurable in the settings. But a heart emoji is probably a good default.