Make CP items (not nav) orderable

[avocadesign]

By default The CP nav is editable and orderable but the list of items in the CP (Collections or Globals for example) is always displayed in alphabetical order.

If you make a custom navigation change to put the most used content at the top of the list in the nav, then there is a discrepancy between the list on the left and the list on the right. That causes visual confusion and I know from training experience that some clients would look to the left an others to the main content. If they go to the main content then they are not getting a prioritised list of items to edit.

It would be great to have control over the ordering of the items in the main content panel.

This is tangentially related to the discussion on idea #1170 about CP customisation options