Added pom.xml configuration to integrate ADAL with Maven based projects

Fixes #56. Artifact is .AAR android archive including both compiled classes and resources.

Prerequisites:

- Maven v3.1.1.
Download: http://maven.apache.org/download.cgi

Usage:
- Execute ```mvn install``` in the root directory containing ```pom.xml``` to create ```adal-0.5-alpha.aar``` library and install it into your local Maven repository.
- Execute ```mvn package``` in the root directory containing ```pom.xml``` to create ```adal-0.5-alpha.aar``` library.