fix: when 'filling in' remaining pokemons that user hasn't selected yet, make sure none of those pokemons have already been selected

[henrylin03]

eg

• imagine there are only 4 pokemons that need to be displayed at once (not 10), and we show maximum 1 pokemon that has been selected before (not 5)
• if user selects pokemon A and B already, we need to fill in the two remaining pokemon spots
• what should be displayed is "A", "c, d, e". "B" cannot be shown, otherwise it breaches our requirement that only max 1 pokemon that has been selected before can be shown (and vice versa if "B" is randomly selected to be shown, "A" cannot be shown as well)
• however, at the moment, because the rest of the pokemon IDs are truly "random", then we might get the scenario where "A", "B", "c", "d" are shown, which is wrong and makes the game more difficult for the player than it needs to be

this likely just involves adding in a check in regeneratePokemonIds method in Gameboard component