Added the beginnings of the XCTest implementation.

Added the new testing target and the scheme as well as some simple tests.
Merge remote-tracking branch 'origin/master' into Test-Integration
Added tests for adding a user, logging that user in, and logging that user out.
Added tests for ApigeeCompositeConfiguration class and updated the User test.
Added ApigeeMonitorSettings tests.
Updated ApigeeMonitorSettingsTests.
Added new tests and updated them along with the test structure in the project.
Added the ApigeeEntityResponse tests.
Merge pull request #84 from apigee/Test-Integration

Test integration