Add useMemo call to useLocalStorage so that the value returned only changes if store actually changes.

[alnorth]

At the moment if a component that uses useLocalStorage rerenders then useLocalStorage will call JSON.parse(store) as a result of the rerender. The value of store won't have changed, but the new call to JSON.parse will mean that a new value is returned with identical contents to the old value. Any hooks then using that value in their deps array will then have to be run again, even though the actual data is the same.

I've updated useLocalStorage so that it uses useMemo to avoid repeated calls to JSON.parse with the same store value.