client/existing: show only user’s reservations

Or all reservations if it is an admin user.
server/auth: remove unused AuthenticatedUserId
server/api: only delete reservation if permissions

That is either user is the owner or is admin.

Also, show better error when given reservation does not exist.
server/api: only finish/update reservation if permissions

Also show better error when reservation does not exist.
server/di: fix default error handling
client: show status code in errors
existing: show past unfinished reservations
client: fix the loading indicator
client: show loading indicator for route changes
client/reserve/success: remove edit btns, pdf links, fix car name
clien: nicer page titles