Deleting textures and materials inserts more than one action to undo stack

There are various ways to delete materials and textures:

• From material/texture editor '-' button
• From context menu in material browser
• Hitting delete key to delete selected material/texture in material browser
• Deleting via navigator (this works as expected)

If the material/texture that is deleted is in use, the references to the material/texture are also removed. However, in all cases except deleting via navigator, the undo stack will get more than one entry for deletion as deletion and reference removal actions are stacked separately. 

In all cases, the deletion needs to be done inside a transaction.