Use same API for testing anything

[aurelien-baudet]

Currently OghamAssertions only provide assertions for JavaMail and SMPP.
However, it could be great if the same code for checking adapts to any other sender implementation. For example, testing an email sending with SendGrid should hide WireMock complexity and let developer use same code as for JavaMail to ensure that email is correctly received.

If this is done, code for checking in classpath testing will be easier to maintain.