make Project#destroy permanently delete all associated records
make Project#destroy permanently delete all associated records

Two benefits:
 - we avoid conflicts in destroy callbacks of various nested objects
   (acts_as_list callback might have also been the culprit)
 - much faster and consumes less memory

ccarruitero/teambox,nfredrik/teambox,wesbillman/projects,vveliev/teambox,crewmate/crewmate,rahouldatta/teambox,nfredrik/teambox,crewmate/crewmate,rahouldatta/teambox,alx/teambox,vveliev/teambox,nfredrik/teambox,rahouldatta/teambox,codeforeurope/samenspel,teambox/teambox,irfanah/teambox,irfanah/teambox,ccarruitero/teambox,alx/teambox,nfredrik/teambox,irfanah/teambox,wesbillman/projects,irfanah/teambox,teambox/teambox,vveliev/teambox,vveliev/teambox,crewmate/crewmate,teambox/teambox,codeforeurope/samenspel