Added Grayscale and Marrakesh schemes

Addes the Grayscale and Marrakesh color schemes. 

Grayscale is a monochromatic scheme, with various tones of gray.

Marrakesh has some "exotic" color combos, like golden-like yellow on dark brown and a vibrant background for the light theme. All the highlight colors were chosen from regular color wheel intervals (like triadic, tetradic, split-complementary etc) instead of arbitrary selection, to guarantee a balanced palette. 

Both themes have adjusted lightness values for good contrast and readability between the foreground/highlight colors and the background with both the light or dark backgrounds. It was achieved converting the hex colors to CIE-L*A*B* and ajusting the L* (lightness) values before converting back to hex. 

Screenshots

Grayscale Dark 
![monodark](https://f.cloud.github.com/assets/6315043/2269797/f83fe5a0-9ee0-11e3-9762-6c44a9f40cff.png)


Grayscale Light side
![monolight](https://f.cloud.github.com/assets/6315043/2269800/008b82dc-9ee1-11e3-9cf2-bd0dd5562460.png)



Marrakesh Dark
![marrakeshdark](https://f.cloud.github.com/assets/6315043/2269803/0827f87c-9ee1-11e3-898d-82a73a2dc211.png)



Marrakesh Light
![marrakeshlight](https://f.cloud.github.com/assets/6315043/2269822/52cfc7e2-9ee1-11e3-9e8d-04f8bc8bfca7.png)