Support global variables

Add a new table that hold globals vars. their values can be accessed by all players and will be used to make navigation options available for everybody if they work together

Start by inspecting the repository's persistence model and the code handling players and navigation options; the issue does not name specific files or tests. Determine how a global variable table should be represented and exposed to all players. Done means shared values can be stored, accessed by every player, and used for cooperative navigation options.

Written by the indexing model from the issue text.