First pass at bulk saving fields.
Fix runtime tests
Fix up the core tests to handle new XBlock.
Add new test for error handling in save.

Fix some bugs found while writing these tests.
Move workbench `render` to default XBlock `render`
Add some runtime handle tests.

pep8 fixes
Add runtime test
Rename KVS.update to set_many
Modify XBlock.__delete__ method
Change test so that lines are not skipped
Refactor and improve tests