Recent filter changes on workshop broke filtering on all tabs but sort by job no tab. Filter now working again on all tabs

Added Drag and Drop support for lists and trees. Implemented drag and drop management on following structures so far:

• Structured Lists (trees)
  • Workshop checklists
  • Website structure
  • Standard unit costs
  • standard jobs
• Basic lists
  • Job scheduling (weekly planner)
  • Job scheduling (workshop)
  • job items (modify/complete job)
  • website items
  • unit costs

Generate stock order : option to disallow backordering

(v4.517: v4.516 contained a defect with dnd functionality on tree based lists that only occurred when testing against older versions of postgreSQL.  Anti recursion SQL test was broken on 8.4 versions of database meaning dnd functionality didn't work for tree structures.).