xblocks: Add XBlocks in requirements
xblocks: Add XBlocks in requirements

Added:
* mentoring
* image-explorer
* dragndrop (v1/v2)
* ooyala
* group project
* discussion
* adventure

edx-solutions/edx-platform,edx-solutions/edx-platform,edx-solutions/edx-platform,edx-solutions/edx-platform