begin work on connection look: Default; Vanilla; Thin

[AlexMitchellMus]

Convert "thin connections" theme setting into a style combo drop-down.

[timothyschoen]

Is this mergable for v0.9.0? Or better to wait?

[AlexMitchellMus]

I think we should also change Object look to use Style. So maybe we can do both at once in 0.9.1? (but this is now ready to go for 0.9 if we want to dedicate 0.9.1 for vanilla style)

EDIT just did this & iolet spacing! :smile:

This gives us identical options as having square_iolet & square_object individual options:

Style	Optional name	Iolet look	Object look	Note
Default	Default	round	round
Square	All square	square	square
Fangs	Round & square iolet	square	round
Max	Max	round	square
Vanilla	Vanilla	square	square	PD-Vanilla iolet spacing