option to add ds9mask

[twshimwell]

MakeMask.py has the ds9mask and it might be handy to add this as an option in the pipeline to e.g. help situations where masking goes wrong or to force it to always mask some regions.

[twshimwell]

Ah this is an option :)

[cyriltasse]

Great issue :))

[twshimwell]

haha well we dont have great functionality for this as the commit that did this is dodgy 0ef400be90b0c9e96ab525e5ff7a7ee93e773af0

A least its not restricted to just circles ;) But you cant make use of red and green for adding/removing things from the mask.

So maybe ill reopen so we can get some better manual masking as i think its good to be able to add or remove.