digital_electricity: save and load configurations

• Used GCComboBox instead of GCDialogBox
• Previous configuration is saved and loaded on start
• changed variant -> var
• Removed "totalComponents" which is obtained by imageName.length
• removed "changeMode()" the tutorial level is left to the previous level when changed from Tutorial Mode -> Free -> Tutorial Mode

Signed-off-by: Rudra Nil Basu <rudra.nil.basu.1996@gmail.com>