- Add test content library XML.

- Ensure that only a course import is saved to the draft branch and then
published. A content library has only a single 'library' branch.
- Add a fields parameter to the create_library call so the call has the
correct number of parameters.
- Add tests which import content libraries using different test methods
and with different branch settings.
- Add test which imports a content library and then exports it.
- Use XBlock module version that supports XML-serialized String of None.
- Add re-import of content library and equality comparison to test.
- Allow get_items to be called on LibraryLocators.

requirements/edx/github.txt

@@ -70,7 +70,7 @@ git+https://github.com/edx/rfc6266.git@v0.0.5-edx#egg=rfc6266==0.0.5-edx
 git+https://github.com/edx/lettuce.git@0.2.20.002#egg=lettuce==0.2.20.002
 
 # Our libraries:
-git+https://github.com/edx/XBlock.git@xblock-0.4.4#egg=XBlock==0.4.4
+git+https://github.com/edx/XBlock.git@xblock-0.4.5#egg=XBlock==0.4.5
 -e git+https://github.com/edx/codejail.git@6b17c33a89bef0ac510926b1d7fea2748b73aadd#egg=codejail
 -e git+https://github.com/edx/js-test-tool.git@v0.1.6#egg=js_test_tool
 -e git+https://github.com/edx/event-tracking.git@0.2.1#egg=event-tracking==0.2.1