Add Manager and Communicator, with MockCommunicator.

Created StackOverflowManager as facade, and Stack-
OverflowCommunicator to interface with SO's API.
Created MockStackOverflowCommunicator to plug in
to tests instead of actual app logic class.
Call searchForQuestions(topic:) in Manager -fetchQuestionsOnTopic(topic:).
Merge pull request #3 from SixFiveSoftware/tests/CreateManagerAndCommunicator

Tests/create manager and communicator