Rename "milestone" to "period".
Fix compatibility of Material objects with url_for.
Do not explicitly require us to use the .id of virtual items, for symmetry with the rest of Rails.
Fix alignment issue on period generator.
Move Lesson Plan controls into dropdown menu.
Merge branch 'lessonbin' of github.com:fuzzie360/coursemology.org into lessonbin
Fix issue that could cause headers to "stick" instead of expanding/collapsing.
Add more space to the "Lesson Plan" span.
Use icons for file upload/folder creation buttons.
Allow generating zips with all materials in a folder or just that particular folder and exclude subfolders.
Fix highlighting of the new button when clicking on it.
When downloading a zip, if stuff are checked, only download those; otherwise download only the files in the current folder (for efficiency purposes)
Merge branch 'lessonbin' of github.com:fuzzie360/coursemology.org into deployment