Add spinner to slickgrid when loading order budget items

[nvernooy]

At the moment budget items are loaded into the slickgrid in the background when the user checks a node in the tree. But if a node has a lot of budget items it is still loading when the user goes back to the slickgrid. Somehow there needs to be a spinner then as with resource/supplier selection.

[nvernooy]

A possible solution, putting it here before I forget it. Using a kind of counting semaphor, increment it when a node is checked and decrement it when the result is returned. When the user switches to the grid and the semaphore > 0 run the spinner, when the semaphore == 0 stop the spinner.