feat(*): Expect a `DEFAULT_FROM_EMAIL` environment setting
feat(common): Implement a shortcut for template email sending
feat(common): Introduce an empty base template for emails
feat(accounts): Send a welcome email to new users
fix(common): Split email tests for each scenario
fix(*): Drop `EmailTestMixin`
fix(common): Document the `DEFAULT_FROM_EMAIL` env variable
Merge pull request #24 from brasilcomvc/feat/email-sending

Feature: email sending