[#47489103] store when age was estimaged
remove oj gem
[#47489103] calculate age
[#47489103] avoid age < 0
[#47489103] DRY specs
[#47489103] rename method to age_for
[#47489103] memoize ages
[#47489103] remove placeholder code
[#47489103] rename AverageAge to Age
[#47489103]refactor scope refinning to a concern module
[#47489103] comments
[#47489103] add api to get average_age
[#47489103] Add v0/contacts/calculate/average_age

New API. Will return average age of all contacts in given scope.
Scope is defined with same parameters as v0/contacts#search

Also removed spork from dependencies and specs configuration
fix bday notificator spec
fix 2nd run specs