Added support for jump_to_id links. Refactored jump_to and jump_to_id into private function.
Added content selector to tests and copy-pasted content stub for links test
Added tests for jump_to and jump_to_id links processing
Made html excerpts multiline
Removed XBlockData as mostly useless.
Refactored tests to simplify getting answer for usage_id
Fixed styling issues
Merge pull request #9 from open-craft/eugeny/jump_to_id

Added support for jump_to_id links