Converted the `state.rs` into an Error enum version of result.

Makes use of the `Error` enum to handle errors. This is a better way to handle errors in Rust. It is also more idiomatic.

Uses js-sys to interact with the Javascript VM, to obtain Date() reference.

Makes use of the most recent save state support in EmuKit.
Thumbnail image support.

There was no implementation to execution mode flag and loading the state in a halted situation was breaking the emu.

Support for MBC3 and MBC5 in state.
Renamed dumps and loads methods.

Made VRAM update possible.

The wrong value was being store in 0xFF50.