See description

1. Created two services for constants and enums, though the
implementation is rather simple (value can be changed...), but since
it's a small man project, so it should be enough.
2. Refactored the logic service, added some new functions to reduce
replicated codes.
3. Refactored the ai service to reuse codes from the logic service and
fixed a previous bug.
4. Updated comments and variables in order to be more clear.
5. No empty image will be shown on the light square since it's useless.