Add email-spec, refactor user_mailer unit test

- use email-spec in user_mailer_spec.rb
remove unused @greeting from user_mailer.rb
refactor welcome email acceptance tests to use email-spec
add style to welcome email

- development.rb now uses mailcatcher
add receives_weekly_email to users

- boolean, default by false
implement weekly email summary
implement user receiving daily email with new claims
Merge branch 'email'