New theme: Konsolas

[chrivers]

This PR provides a new theme, Konsolas.

Konsolas is a carefully hand-tuned themed, aimed towards working in the shell.

In particular:

1. The primary colors (red, green, blue, etc) are true to their names, so that info/warning/error messages make sense by the usual conventions of "red=error", etc.
2. The "dark yellow" color, which in many built-in themes is a terrible olive brown affair, is selected as a more pleasant shade, slightly orange in color, while still feeling like a natural "dark" version of the primary yellow
3. The "dark cyan" and "cyan" colors have similarly been tweaked to be more pleasant and useful.
4. The colors are selected for good legibility for many common combinations of foreground/background.
5. Bold colors are selected to have approximately the same perceived brightness. Same with dark colors.
6. For each color, the combination of bold foreground on the same background (for example, bold red on red background, bold blue on blue background, etc) has been optimized to be easy to read. The most challenging combination is bold-blue-on-blue. The blue background has been selected to be a smidge darker than the other background colors, to ensure bold-blue-on-blue will be legible.
7. This theme is, in my opinion, particularly well suited to text user interfaces. For example, try it with htop, ls -l --color, and fancy zsh prompts.

[mbadolato]

Awesome, thanks!