Enable Extracted XBlocks

[farhan]

In this story we will track the rollout of enabling the Extracted Xblocks in the edx-platform.

• [x] Enable Poll XBlock
• [x] Enable Word Cloud XBlock
• [x] Enable HTML XBlock
• [x] Enable Annotatable XBlock
• [ ] Enable LTI XBlock
• [ ] Enable Problem XBlock
• [ ] Enable Video XBlock
• [ ] Enable Discussion XBlock

Acceptance Criteria

• [ ] Pointer Tag implementation should be tested. XBlock should be Import and Export properly.