Add aantal schademeldingen as unit to map & graphs

[SanderDevisscher]

Currently we actually display the "aantal schadegevallen" instead of the "aantal schademeldingen" (see #421 & #419) if possible we would like to add "aantal schademeldingen" as unit to all wildschade maps & graphs (and rename "aantal" to "aantal schadegevallen")

Some definitions:

• Aantal Schadegevallen = n_distinct(UUID)
• Aantal Schademeldingen = n_distinct(indieningID) => should be less

I'll make sure indieningID is allways provided, it is not atm.

[SanderDevisscher]

As explained in #397 (comment) the definition of
Aantal Schadegevallen is going to change into n_distinct(schadegeval_id) in the not so distant future.

[SanderDevisscher]

Some steps are needed internally see #1039 from the backoffice