Added support for mocha theme

I did this because I like the mocha variant on base16. I use this personally and thought others may like it. I understand it doesnt quite fit with the "spacegray" theme, but giving people another option on theme is never a bad thing. Screenshot below


![](https://github.com/jcomo/spacegray/tree/583c7e80807766c967f9bcb7e14cb28464c74b12/Screenshots/spacegray-mocha.png)