Bookshelf refactoring

The refactoring addresses a number of issues found when trying to add display of an optional subtitle line:

• The book card (and other cards) width and height are passed as props
  • This can (and does) cause incosistencies, where various card containers use different values. For example book cards currently have slightly different size on the home and library pages.
• The height of the card does not reflect the actual card height. the bottom book details use absolute positioning outside the card area.
  • This requires complex layout computation that also happens outside the card, to make the card containers have the correct height to display both the card image and the details below.
• sizeMultiplier is used many times in each of the cards.
  • Wherever some size attribute is set, it is multiplied by sizeMultiplier. This clutters the code quite a bit.
  • The sizeMultiplier is computed differently in each of the cards, although the result should be the same
• bookCoverAspectRatio is passed as prop
  • This can also be computed in a single place.
• There's is a separate itemSlider component for each card type.
  • The Vue templates and code in most component are mostly duplicates.
• The bookshelf scaling of spacing and font-sizes is inconsistent
  • When the scaling changes (by increasing or decreasing the cover size), some of the spacing and font-sizes change, some don't

The following bookshelf fixes and refactoring were implemented:

• The height and width of bookshelf cards is now determined by default inside the card
  • The height of the card graphics (cover image or material icon) has a default.
  • All other properties are computed.
  • the card computed height now includes the bottom description if it has one.
• The shelf height is now determined by the computed height of the cards inside it
  • In lazyBookshelf, where the height needs to be determined in advance, one dummy card of the right type is mounted in order to get its width and height.
  • This makes shelf height calculation straightforward and less error-prone.
• All the itemSliders are now merged into a single component
  • The card component is dynamically determined by the shelf type.
  • Also fixed some small edge case slider scrolling issue, and made it not dependent on the card width
• sizeMultiplier and bookCoverAspect ratio are now obtained from the store
• The scaling and font sizes is now made consistent by changing them to relative em units
  • This is mostly done transparently by changing the default tailwind definitions
  • A version of the original tailwind spacing is still available (by adding r to the spacing number, e.g. right-4r)
  • At the bookshelf level, the font-size is set to sizeMultiplier * 1rem
    • this makes the tailwind classes inside the bookshelf reactive to the sizeMultplier (since they are now specified in em units)
    • this also makes sizeMultiplier multiplication redundant in most places (by changing rem units to em), making the code less cluttered.
• Fixed some buggy booksPerFetch behavior
  • When cover size is set to smallest, lazyBookshelf doesn't get enough books to fill the first page, so something like this appears: This was due to booksPerFetch having static values. It was fixed to have a value depending on the the number of books per shelf and the number of shelfs per page.