Bug 29857: Make the exception classes inherit from the base class

Bug 29857: Make the exception classes inherit from the base class

We have a base class Koha::Exceptions::Exception but it's not used in
most of our exception classes

Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>