Project Tree Collapse

Clicking a folder icon causes content to toggle visibility. Folder
icon changes between 'open' and 'closed', while the content does
a sliding toggle.
Fix project tree animation 'bug'

Some browsers, such as Chrome, have a 'wobbling'
effect when collapsing an empty folder. Decreasing
the duration of the animation to zero for empty
folders makes things look better.
Merge pull request #173 from KSHSK/project-tree-collapse

Project Tree Collapse
Merge branch 'master' into undo