In the "Custom Animation" dialog, all animated objects are listed in the "Change
order" window. Here, to change the otrder of an object, the user has to press
up/down arrow. 

This arrow has two limitations:
1. For each upward/downward move, an arrow has to be clicked. For a long list of
objects, a lot of clicks are required.
2. You cannot select multiple objects and move them together.

Suggestions:
1. Allow the user to select multiple objects and move them together.
2. Allow the user to drag object(s) with mouse to a new location. 
3. Introduce "repeat stroke" function in the up/down buttons: If the user keeps
this button pressed, the objects should keep moving in the desired direction.
This is just like how pressing down on a keyboard key repeats that function.
(For example, pressing on the "k" key will produce kkkkkkkkkkkkkkkkkkkk.)