Refactor the email service to have a common interface for notifications and SMTP
- EmailPasswordResetService uses the appropriate messageService to send emails

[#78676824] https://www.pivotaltracker.com/story/show/78676824

Signed-off-by: Madhura Bhave <mbhave@gopivotal.com>
Connection error from notifications server only ignored on startup

- Also, don't provide default value for notifications.url

[#77585216] https://www.pivotaltracker.com/story/show/77585216

Signed-off-by: Madhura Bhave <mbhave@gopivotal.com>