fix: Allow disabling file name sanitization

[taratatach]

Some clients, like Cozy Desktop, do their own file name sanitization
and don't expect cozy-client to do it for them. In fact, this
sanitization would lead to issues down the road.

To prevent these, we add a sanitizeName option to FileCollection's
methods to disable cozy-client's sanitization.
The option's value will be true by default so other clients don't
have anything to do.