Gradle config update

Adding an additional build type `dev` to be used to install app while in development mode. 

_Basic Gradle Instructions_

Install app using the following command on the command line:
```
./gradlew installDev
```

If the command line displays a permission error - use the following line to resolve the permission issue:
```
chmod +x gradlew
```

Here is the official user guide for Gradle - http://tools.android.com/tech-docs/new-build-system/user-guide