Realigned part of the code (indentation).
Moved the delete customer button to the customer editing page.
Transformed the customer listing from 'cards' to a table, to add headeers and sorting.
Sorting (with direction) has been added for a few fields and it is handled via Session properties, to ensure a consistent view.
Added flash feedback when customer gets deleted.
Session gets flushed upon logout (it doesn't happen by default, which is what I was expecting).