Add SendGrid for mail sending

The application will need to send emails.

We will use SendGrid for handling emails.
Create a service which can send emails via SMTP using SendGrid.

This service have roughly the following parameters:
* destination email address
* email body (text for now - templating will be added with another issue)
* message parameters (variables that can be inserted in the message)

SendGrid configuration data should be easily changeable from application properties