Add favorite property to library items

[Rapha149]

Brief summary

This pr adds the ability to mark podcasts (and other library items) as favorite and allows to filter for favorite items in the library page and the latest episodes page.

Which issue is fixed?

#2968 and #4816

In-depth Description

Added features:

• Star icon next to the title in the item page, clickable to toggle.
• Star icon in the bottom left corner of item covers, when not favorite only visible on hover, also toggles on click.
• Filter by favorite in audiobook and podcasts libraries.
• Filter by episodes of favorite podcasts in the latest episodes page (implemented via checkbox, the state is saved in the cookies like the library filters).

In the database I implemented it by adding a new table with the columns libraryItemId and userId.
I added two new strings: LabelFavorite (en: "Favorite") and LabelOnlyFavorites (en: "Only Favorites"), but I only added them in English and German.
I also implemented these changes in the apps: advplyr/audiobookshelf-app#1826

How have you tested this?

I tested the desktop and mobile version:

• The star icon appears correctly in the item page and in the cover, if present it's also positioned above the ebook format.
• Adding and removing an item from the favorites works.
• Filtering in the library page as well as the latest page also works as expected.

Screenshots

Desktop

Cover:

Item page:

Filter menu:

Latest page:

Mobile

Cover:

Item page:

Filter menu:

Latest page:

[nichwall]

Just an FYI, but web client front-end changes are not actively being merged or reviewed right now because we are in the middle of migrating away from Vue to a new framework. You're welcome to leave this open in the meantime (either as inspiration or if someone else wants to use it in the meantime).