Save state management: save and load played hands

[kleinfreund]

Description

Add a basic save state management system so users can save and load played hands.

Motivation

While a user can technically keep track of multiple played hands already by keeping track of the various share URLs of their played hands, it'd be much nicer to allow users to save the state by name in the their browser (i.e. local storage). They could load their saved states and thus flip and back and forth between various hands to try out which hand performs better.

This should probably be limited to ~10 entries or something like that. There are probably also storage limitations by browsers that I need to consider here.