Enable line annotation label as label sub-element

[stockiNail]

This PR moves label node of line annotation to sub element.

[kurkle]

Took just a quick look on phone. I will try to review properly some other day.

[kurkle]

Not sure why this.rotation and this.options.rotation need both to be used (and the fallback with || might not work in all cases as expected, specifically when this.rotration is 0)

[stockiNail]

Not sure why this.rotation and this.options.rotation need both to be used (and the fallback with || might not work in all cases as expected, specifically when this.rotration is 0)

I thought a little bit more and you're right! This is wrong only when the calculated rotation is 0 and the label options of a line is set to 'auto'.

Maybe the best could be to set element.rotation for all annotations which have got a label, and then use it instead of the options.

[stockiNail]

Not sure why this.rotation and this.options.rotation need both to be used (and the fallback with || might not work in all cases as expected, specifically when this.rotration is 0)

@kurkle I have changed using only element.rotation at runtime of the label.