Change favorites to follow convention of adding shortcuts at launch time

[ericfranz]

This would be slightly more performant, since on each request we wouldn't be checking for the existence of a bunch of directories that do not exist. So we would replace:

osc-ood-config/ondemand.osc.edu/apps/dashboard/initializers/ood.rb

Lines 3 to 8 in bde54e4

	projects = User.new.groups.map(&:name).grep(/^P./)
	paths.concat projects.map { |p| Pathname.new("/fs/project/#{p}") }
	# add scratch space directories
	paths << Pathname.new("/fs/scratch/#{User.new.name}")
	paths.concat projects.map { |p| Pathname.new("/fs/scratch/#{p}") }

with something closer to the solution in https://discourse.osc.edu/t/other-directories-in-files-explorer-app/335

Though the files shortcuts to newly created project or scratch directories would not appear in the menu until the dashboard was restarted.

[ericfranz]

Essentially, we use glob so that we only add to the candidate paths directories we already have verified to exist, instead of all the possible directories.