Change HSL scaling to match 360° convention, add HSV

Merged username-removed-244348 requested to merge RomanHargrave/inkscape:feature_hslInDegrees into master

This patch changes the scaling for HSL color selection mode to match conventional tools, which use a 360°/100/100 model for Hue, Saturation, and Lightness respectively. A new mode, HSV has been added which follows the same convention.

Internally, a new value has been added to SPColorScalesMode for HSV, and the value corresponding to HSL has been renamed to SP_COLOR_SCALE_MODE_HSL instead of SP_COLOR_SCALE_MODE_HSV to indicate that it is, in fact, used for HSL and not HSV.