Sets an Action in the Page's given index
If index is -1, the action will be set in the latest empty index
  overload 1:
                        
Page:setAction(index, action)  
  | Method Property |  Fluent Description |  Representation | 
 | index accepts |  an Integer |     |    
| action accepts |  an Action |     |    
| Return Value |  a Page |     |