Name the players consistently on the frontend and backend

[norbertdragan]

The front-end originally started naming players with 1, as player1. The backend however, starts counting from 0, as player0. This is causing some unnecessary and sometimes confusing code all around the app.

We should fix it and the frontend should begin counting form 0 to match the backend.

[norbertdragan]

A good suggestion is to use constants capture these variable names.