Feature: Allow user to change source in time manager tracks.

Please allow users to change source in time manager track. This is being discussed in

https://discourse.paraview.org/t/time-manager-advanced/15217

To copy the discourse verbiage here,

I have a user that wants to change sources inside of the Time Manager. The reason is he is creating fairly complex pipelines, with numerous datasets turning visibility on and off. When he decides to change/add a filter, and move where the visibility controls are found, he has to re-input these controls. So, the feature request is:

• Add can.exo
• Add a clip filter
• In the Time Manager, add a Clip Filter/ Visibility track. Make visibility go from 0 to 1.
• Add an Extract Surface filter. Have it’s input be can.exo.
• Change the clip filter’s input to be Extract Surface filter.

Now the new feature request.

• Change the Clip Filter/ Visibility track input to be Extract Surface.

If the variables are not the same between the two filters (such as slice plane location), just change to the default variable.

One suggestion is to change this in the top of the Animation Keyframes dialog, where it shows Input and variable.