Displays a dialog for defining variables.
The displayed functions are: 
•	Insert
	Inserts the variable in the entry column of the variable list .
•	Clear
	Clears the selected variable.
•	Change
	Changes the selected variable.
•	Open
	Opens a variable list. The existing variables will be overwritten.
•	Add
	Attaches a variable list. to the existing list.
•	Save
	Saves the variable list under a new name.
Note:
1.	Variables can be created from other variables.
2.	Variables always have the following construction:
	<variable name> = <definition>