Implement skeletal code for virtual workbin folder support.
Implemented listing virtual folders.
Display milestones sorted by date, not creation time.
Merge branch 'lessonbin' of github.com:fuzzie360/coursemology.org into lessonbin
Try (and failed) to implement the tree display for virtual folders.
Merge branch 'lessonbin' of github.com:fuzzie360/coursemology.org into lessonbin
Implement is_virtual for physical materials also
Implement a virtual folder for trainings also.
Move the show/hide buttons per milestone to the header.
Change "Date Uploaded" to "Date Added".
Link virtual folders to the root of their course workbin.
Make sure students can only see the missions and training files for missions and trainings they can see.
Merge branch 'lessonbin' of github.com:fuzzie360/coursemology.org into lessonbin
Exclude virtual folders from the Lesson Plan file picker.
Introduce explaining variable.
Sort folders by name, with virtual folders first.
Sort folders before files.
Sort by name in folder listings.
Merge branch 'lessonbin' of github.com:fuzzie360/coursemology.org into deployment
Merge branch 'deployment' of github.com:fuzzie360/coursemology.org into deployment