Informative git prompt for bash and fish

This prompt is a port of the "Informative git prompt for zsh". A bash prompt that displays information about the current git repository. In particular the branch name, difference with remote branch, number of files staged, changed, etc. The advantage of this approach is, that you only need to specify the parts, that are different to the Default theme. You can set the GIT_PROMPT_SHOW_UNTRACKED_FILES variable to no or normal to speed things up if you have lots of untracked files in your repository. This can be the case for build systems that put their build artifacts in the subdirectory structure of the git repository. Setting it to all will count all untracked files, including files listed in .gitignore. The most settings are now stored in theme files. To select a theme, set the variable GIT_PROMPT_THEME to the name of the theme located in <INSTALLDIR>/themes without the extension .bgptheme.