add stylesheet dependency

[hannesdelbeke]

• now can run outside of unreal, e.g. in blender
• now uses unreal stylesheet dependency. so we don't need to update this repo, and the stylesheet repo, and the unreal plugin repo, instead we can just update the stylesheet, and all other repos auto update
• added support for unreal_style_sheet.show()
• fix bug with incorrect package name. changed unreal-script-editor to unreal_script_editor and updated toml.
• tested installing and building wheel from toml, now installs correctly

just for test purposes, tried it without the stylesheet enabled. this is not part of this PR.
but shows that the tool can run without stylsheet, or with another stylesheet.

blender stylesheet	unreal stylesheet

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