Adding game listing by platform

There was already a basis. Since i don't know if it was already in use, i used it as a basis for a new Api more in line with naming conventions for other API's.

Made it so that the list is by platform Id. Developers have that id by fetching the list of platforms. Fetching by name makes future conflicts etc possible

issue https://github.com/TheGamesDB/TheGamesDB/issues/83