Add action for deleting contributor as well as helper methods to determine if contributor can be deleted.
Add action for deleting contributor as well as helper methods to determine if contributor can be deleted.

samchrisinger/ember-osf,cwilli34/ember-osf,crcresearch/ember-osf,baylee-d/ember-osf,pattisdr/ember-osf,samchrisinger/ember-osf,pattisdr/ember-osf,chrisseto/ember-osf,binoculars/ember-osf,hmoco/ember-osf,jamescdavis/ember-osf,jamescdavis/ember-osf,CenterForOpenScience/ember-osf,binoculars/ember-osf,hmoco/ember-osf,CenterForOpenScience/ember-osf,baylee-d/ember-osf,cwilli34/ember-osf,chrisseto/ember-osf,crcresearch/ember-osf