Implement outcold theme

This theme is based on ys theme with some modifications:
* Show more information about git status
* Show error code from previous command if it is not 0
* Less distractive PROMPT 

In additional I've included `$ZSH_THEME_GIT_PROMPT_NO_DIFFERENCE_REMOTE` which helps to show when remote is equal to current.

![Screenshot](https://dl.dropboxusercontent.com/u/114202641/Public/outcold.zsh-theme.png)