Use State `select` on "Edit Order" page

As @ChromeOrange reported in #5875 the plugin could use a Select Field just like it happens on the front-end.

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My only question is if I should use `Chosen`? As of right now almost all other admin are using it.

**Note**: All the Commits `WP Code Std` are meant to fix things that my WordPress PHP Code Sniffer is bugging about .