Allow multiple games in the viewer

Here some thought about what is the goal, what the options are, and what the usage will be. See ticket 12

Goals

• Allow more than one gamen in one view to be shown.
• Allow switching from one game to the other.
• Not (currently): keep the context (move played, but should be easy to add later)

Options

• visualize the list of games by a dropdown ==> done
• (visualize the list of games by an additional list) not really necessary, only if the reader would be like a database (which is not). So no search, no filtering, ... and therefore no need to have additional place wasted for the list.

Usage

• Use the same parameters as the viewer has.
• Add one more parameter (many games == true)