Allow external initialisation of the SSL context for smtps

[FillipMatthew]

fixes karastojko/mailio#173

These are the changes for the smtps class that allow for the creation and initialisation of an SSL context externally to the library so that users can setup their SSL certificates or other settings that are not accessible when the context is kept private.

The default was also changed to use peer verification by default.

These changes should be easy to also apply to the other classes that need them.