feat(script): support to add additional games from local or web

[adglkh]

Without modifying the install script, this enables people to add additional games to the cloud gaming demo through an manifest file.

On the Web UI, people still need to modify the code a bit to display the newly added games for the showcase.

[morphis]

As discussed we should not touch the install script for this but instead describe in the documentation what changes people have to make to get new games added.