Slider Label and Value feature, rgba and kelvin color fixes

[lenadax]

Currently used Version: 5.5.2

Description

This PR describes a feature that implements a label and an editable input field for the iro.js Slider component.
See the corresponding PR for iro.js: jaames/iro.js#229

Changes

• add logic for user input in new input field option - currently this is limited to typing, and pasting from clipboard.
• new property sliderLength:
  Since iro.js has a sliderSize option for thickness, but no option to manually set slider length, I added an option to it.
  This also makes the layout prettier and more contained when using the input field option added in the iro.js repo.
• new property showInput:
  This property renders an input field next to a slider. ActiveColor Value can be set with this input.
• new property showLabel:
  This property renders a label next to a slider.
• new property disabled:
  Disables the input field.
• getSliderDimensions now returns the correct width when using with my input field or when manually setting slider width.
• color.ts: IroColor now defaults rgba.a value to this.alpha instead of 1. This solves the Issue (RGB and Alpha sliders not keeping alpha value on interaction  jaames/iro.js#227) I posted for iro.js.
• color.ts: kelvin conversion now returns a more accurate value when calculating from and to rgb.