Create notifiable concern and refactor project observer
Refactor contribution observer
Use single include on contribution and project models
Add missing param to notification when project is finished
Improve if statement readability on contribution observer
Use simple merge method on contribution observer and notifiable concern
Use Configuration without '::' from '::Configuration'
Fix missing params to contribution observer on project notification
Merge pull request #270 from neighborly/jl-refactor-observers

Refactor contribution and project observers
Define payment observer class
Add missing fields for payment on match

Fields:
  - Key: We send emails to users showing that key, if the user has some problem
  and needs to contact us, they can use that key to identify the payment.
  - Confirmed_at: When we confirm the payment, we set the current date time to
  be able to debug payments using time.