add new API method to collect statistics about users social score in a c...

...ourses discussion environment


@martynjames since you know some Ruby, can I ping you on this. I'm sure there are nicer ways to do this in Ruby, but this seems to give us what we want
If this is working as expected then it's fine
 - just seems odd that the symbol syntax :subscriber_id is being used, but then an object member is being referenced. Just seems odd wrt :subscriber_id.ne vs subscriber_id.ne (The second is a string lookup on the value of subscriber_id.ne; first suggests a symbol lookup, but it might simply convert into the string lookup by virtue of calling the member... not sure)