fix(themes): fix potential command injection in `pygmalion`, `pygmalion-virtualenv` and `refined`

The pygmalion and pygmalion-virtualenv themes unsafely handle git prompt information
which results in a double evaluation of this information, so a malicious git repository
could trigger a command injection if the user cloned and entered the repository.

A similar method could be used in the refined theme. All themes have been patched against this
vulnerability.