More customization

This new base script (`git-info.sh`)
* is not related to a prompt shell anymore
* is using configurable color codes
* doesn't leak variables
* does not depend on external configuration
* offers configurable color codes per symbol
* has a more understandable name, that can be easily used in another context (I'm using it in my own crafted oh-my-zsh theme, though it's named `oh-my-git.plugin.zsh`)
* adds suffix and prefix config
* can toggle the display of the git repository symbol (`display_git_symbol`)
* can toggle if empty spaces for off flags will be displayed (`use_color_off=false` and flag is off, toggable with `print_unactive_flags_space`)
* can be toggled per git repository config `git config --get oh-my-zsh.hide-status`
* displays current git action (`REBASE-i`, `REBASE-m`, `REBASE`, `AM/REBASE`, `MERGING`, `BISECTING`, `CHERRY-PICKING`)

Note default color codes might not work well on ZSH, when this method is echoed on `RPROMPT``, use the following ZSH compliant color codes.

For example: 
```
# redefine zsh compliant color codes for oh-my-git
omg_on="%B";
omg_off="%b";
omg_red="%F{red}";
omg_green="%F{green}";
omg_yellow="%F{yellow}";
omg_violet="%F{magenta}";
omg_reset="%{%f%k%b%}";
omg_prefix=" %{%B%F{green}%}[%{%f%k%b%}"
omg_suffix="%{%B%F{green}%}]%{%f%k%b%}"
```