close HTML tags properly
use <br> instead of <br \>

We are serving it as HTML5
use data-fancybox-group instead of rel to define fancybox groups

Using rel causes validation errors.
remove outdated comment
close HTML tags properly (2)
make bar urls consistent
reverse bar log entries through a separate page instead of a form

The bar log contained a form with one submit button for each log entry.
This was used as a button to revert the log entry, using the buttons value
to store the id of the log entry to be reverted.

This commit changes the revert button to be a link to a new page,
/bar/reverse_<bar entry id>, which will delete the entry and redirect to
the bar log. If the argument 'prev' is sent along with the request
the page will redirect to this url. This way we can ensure the user is
sent back to the exact page she was on when clicking the revert button,
including pagination and filters.
bugfix: delete linked transaction when deleting a bar log entry

When a bar log entry is deleted (reverted) the corresponding cash
transaction or bar account transaction needs to be deleted too.