Added Mail Filter Features

Added a separate class (to keep the core of the project clean for those who don't need it) that will allow the developer to add few more useful filtering functionality to the mail reader class.

The Developer will be able to code few more lines and leave the rest to the class. Tried to add as much comments to the code to make it clear and we can then further work on it to add more features and even making this simpler.

Appreciate your acceptance and merge :)