Avoid putting remote objects in the store

[CharlieHess]

When getState is called from the renderer, what it's actually doing is creating an object in the main process. When we iterate that object for cloneDeep, each property look-up translates to an ipc.sendSync (this is similar to the situation in electron/electron#3856). We can avoid this whole rigmarole if we just use a primitive type, so instead, we'll stringify it.

This does add the requirement that everything you put in the store must be serializable (reasonable IMO). If you stored something like an Error or a RegExp this would break down.

[samiskin]

Lgtm!

[samiskin]

Though I'm not sure about the "everything you put in the store must be serializable", as theres currently actually an issue regarding that #32

[samiskin]

I'm not sure if there's a way around that though, and I think thats currently a problem anyway. The only thing I can think of would be to have the initial state also have to be filtered, but then that poses the problem of anything not passing the filter being undefined at the beginning instead of the initial value.

I'll leave the decision of whether to look into that to you by leaving the merging to you 👍

[CharlieHess]

@samiskin yeah I'm OK with it as it doesn't regress existing behavior, just makes it more explicit.