add img in edit mode. Qiu
make the lessonplan items as a partial. Qiu
finish image uplouding
finish uploading sb file
fix link on homepage. Qiu
add sb file icon
fix large image in steps
add cucumber test for view lesson
add some document to setup environment on the Mac
remove the navigator on the lesson page
change the picture size in the introduce of lesson plan
fix the lesson attachements display bug
fix the thumbnail bug for images excpet jpg
fix the discussion link bug in lesson attachement page
fix the attachments and discussion count updating problem
custom the title of file uploader
refactor attachement model
implement remove function of attachement
add authentication for removing attachement
refactor CommentResource and AttachmentResource