Allow users to make predictions

This PR allow users to make predictions from dashboard.

Predict button can be places anywhere using the following format:
```erb
<button type="button"
               class="btn btn-primary btn-sm btn-predict"
               data-host="<%= match.host_team.name %>"
               data-host-flag="<%= match.host_team.flag %>"
               data-rival="<%= match.rival_team.name %>"
               data-rival-flag="<%= match.rival_team.flag %>"
               data-match="<%= match.id %>"
 >Predict</button>
```