Mod7

## Features
- Invite a friend feature

## Refactoring
- Method renaming for readability
- `rating=()` bug fixes for QueueItems review creation and updating rating
- Move email smtp settings to mailgun
- Seed and schema modifications for compatibility with PostgreSQL

## Concerns
- Tokenable concern

## Tests
- `user_resets_password` feature spec
- `user_invites_friend_signup` feature spec
- `generates token` shared example