[POC] track_visibility attribute copy when create related field

[zaoral]

NOTE: This issue comes from https://github.com/Vauxoo/yoytec/issues/1830#issuecomment-239344783

track_visibility attribute is been copy/inherited when we create a related fields from the original one.
We think that should not inherit the track_visibility attribute for many reasons, one of the more important is when we have a:

• A field modelA.field_a with track_visibility='always'
• A field modelB.field_b related field to field_a

If modelB has not mail.thread, this will throw an error.

This issue (soon converted to PR) will add a dummy change the illustrate what is going on

Best Regards