qtype admin: MDL-18425 also related to MDL-18355.

qtype admin: MDL-18425 also related to MDL-18355.

Allow question types  to be displayed in order that is better than random or alphabetical. Since we don't know all the qtypes there may be:
1. Store the order in the DB (config plugins).
2. Set up a good default order for the standard types. (Unknown types go at the end by default.)
3. Allow admins to edit the order on the qtype admin screen.