Feature/gcstaskservlet

This is a *ServerTaskServlet* that runs *ServerTasks* (abstract)

The following *ServerTasks* have been added
 - AddPublicReadObject
 - AddPublicReadBucket
 - RemovePublicReadObject
 - RemovePublicReadBucket

There's also a class that is dedicated to handling bucket iteration.  It takes a list request and executes some kind of update request (also passed into the constructor) on every object found in the list.  

JUnit unit tests are included for the classes as well as casperjs e2e tests.  The e2e tests actually run an external anonymous get request (using cURL) to confirm whether an object has public read or not.

The end result is a task call something like this:
https://the-storage-appengine-server/servertask?task=AddPublicReadObject&bucket=abcdefg&object=myfile

or

https://the-storage-appengine-server/servertask?task=AddPublicReadBucket&bucket=abcdefg

@EnlightenedCode @fjvallarino please review