Fix numepad 0 key and add few other keys

The scan code of the numepad 0 key is 98, not 88 since that correspond to the scan code of KP_ENTER.

I took the opportunity to add the missing numepad keys like KP_PLUS, KP_MULTIPLY, etc...

Some other keys like caps lock weren't properly detected either.
Merge pull request #2234 from Noxalus/incoming

Fix numepad 0 key and add few other keys