Allow enviroment variables in launcher commands

Allow the "Command:" field in the "Edit Launcher" dialog window to support environment variables for commands.\

For example, instead of
"/home/username/rest-of-path/application-name"
it would also allow
"$HOME/rest-of-path/application-name"

This would cover all of the following which use this "Edit Launcher" dialog
-Menu (For example Whisker Menu)
-Docklike Taskbar launchers
-Panel launchers
-Desktop icons

EDIT:
This would also apply to "Keyboard - Application Shortcuts" tab, where commands can also be launched.

Thank You