mavenization, restructuring project into 'library' and 'demo' folders

If you want to build with maven you need to:
- locally install newest support library using
android-maven-sdk-deployer
- locally install date4j library jar
(or deploy them into some public repo like Maven Central)
deleting DS_Store
Merge pull request #52 from destil/replace-joda

Mavenization, restructuring project into 'library' and 'demo' folders, fix for #50