Change behavior of add to cart button
Fix add button alignment
Add 'drop all' button.
Teeny-tiny table buttons
Fix #11.

Someone (me) changed the cart's id to be a class, thus breaking the
'Einkaufswagen' tab.
Add placeholder string to filter field
Change button text

Multiple people reported that 'abschicken' sounds too final, as if it
were to be printed immediately. This changes the text to 'Speichern'.
Add link to github-pages to README