Added support for building project using gradle.

[farrukhnajmi]

Added support for building project using gradle. Changes are backward compatible and still allow building using Eclipse and old style project structure.

Consider pulling this request to allow others who use gradle for builds to more easily contribute to this project. Eventually it is suggested to change project structure to match the new project structure used by Android team and the default for gradle projects.

To build project using gradledo the following:

cd .../ExtendedCalendarView/ExtendedCalendarView ./gradlew assembleDebug

[farrukhnajmi]

I have one more commit that I would like to create a Pull request for. Before I submit that I would like to hear some feedback on this Pull Request. Thanks.

[JerellDR]

Is there a way for me to clone from this unmerged pull request? I'd like to be able to build using gradle.

[tyczj]

One of these days I will get around to doing this and testing it I have just been busy