Upgrade dependencies

Specifically Rails to 4.1.7 and RSpec to 3.1.0.
Update to conform to ABC metric cop
Upgrade to latest ruby release 2.1.4
Ensure DualOwners#valid_owner outputs correctly

Code review pointed out that previous implementation would infact
provide errnonous message output. The new implementation creates
messages from symbols of parents that should exist against their
actualy availability from the child model.
Rename and refine DualOwners concern to Parents

This allows for models to have any number of potential parents and
still have validation check to ensure only one is populated.

This also allows for the possibility of X parents to be populated in a future validation should we require it.