overload the __setter__ in DiffractionObject to correctly update arrays

[sbillinge]

Problem

the all_arrays attribute can be updated with anything right now. this could inadvertently lead to invalid arrays.

Proposed solution

We would like to block this so it can't be updated (issue a warning?) and these arrays only updated by insert_scattering_object

do this by defining an @Property for this attribute.

There may also be some other behaviors we want to modify to ensure valid __set__ behavior