Update ProxyConfiguration::writeConfigurationToDevice for KitKat

Update ProxyConfiguration::writeConfigurationToDevice to work with the new ProxyProperties constructors added in KitKat. This change requires an update to the version of Android being used to build the library, in order to avoid hard coded SDK values.

Addresses [issue 8](https://github.com/shouldit/android-proxy-library/issues/8).

It looks like the entire ProxyConfiguration.java file was changed; however, this is because that file had carriage returns in the file. Let me know if this was intentional and I'll modify the file accordingly. For clarity, the relevant change modified lines 451 - 453 to be:

    Constructor constr;
     if (Build.VERSION.SDK_INT < Build.VERSION_CODES.KITKAT) {
         constr = ProxyPropertiesClass.getConstructors()[1];
    } else {
         constr = ProxyPropertiesClass.getConstructors()[3];
    }