* Translation string for error notification
* Use function instead of a link for paypal
* Inject notification service, function to check the amount of gems to purchase, function to handle payments with paypal
* Throw error if amount of gems is zero or negative
* Add condition to raise error if amount is negative
* Added gem errors for gifts 0 or less
* Fixed linting and broken test
* Fixed test syntax
* Added back needed strings
* Fixed group locales
* use new email template when subscription is cancelled from joining a group plan
* use new email template when subscription is cancelled from joining a group plan - needs more code, tests
* change from sending new email as a cancel-subscription option to sending as a group plan join email
Uses a new group-member-join email template instead of old group-member-joining because new template includes mandril conditional merge tags.
Also adds tests and comments. Edits some comments for accuracy and typo fixes.
* adapt group-member-join email template for manual cancel message for iOS and Android subscriptions
* save test user so its profile name can be read by calls to sendTxn
* add documentation for the user model cancelSubscription function
* add constants for strings passed to mandrill email templates
