Add some color mode icons for Okular

These are the icons from T12825. They are intended for a Color Mode menu, which is being created in graphics/okular!141 (merged). Intended usage:

(Image displays old versions for Invert Lightness and Invert Luma icons.)

Multi layer icons are no longer included, see graphics/okular!223 (closed). davidhurka/overlay-icon-engine-demo> demonstrates how they would have worked.

• 1: color-mode-black-white (Intended for Change Dark & Light Colors and Convert to Black & White)
• 6: color-mode-hue-shift-positive
• 7: color-mode-hue-shift-negative
• 8: paper-color
• 13: color-mode-invert-image (Intended for Invert Lightness)
• 16: color-mode-invert-text (Intended for Invert Luma)

The hue shift icons are difficult to compose. Neither scour nor svgcleaner can handle these styles in a useful way, so I joined the existing colormanagement icon and the arrows in a text editor. I hope you like them. :) If not, how about this idea: Draw three squares in a row (red, green, blue), and below them an arrow pointing left or right. That shouldn’t be any difficult.