Exclude file "local.properties" from version control

[alexhauser]

Please exclude the file "local.properties" from version control, it prevents the project from building on systems with a different sdk path. By removing this file manually after cloning the repository, I was able to build the project just fine in Android Studio.

Btw, thanks for the example code, it was just what I was looking for!

[kpbird]

@alexhauser Thank you for suggestion, I will take care next time.