Command line action with temporary files

The action would have two fields:
fields[_t('Command')] = self.CharField(' ')#should be a space not empty string

The command line should contain for example in.png and out.jpg. With a regular expression you can find a filename with in.* or out.*
Phatch should than save the temporary file as requested as in.* and open (&delete) the out.* Use the tempfile module for temporary files. Use the named temporary files. See core/lib/libtiff.py for an example:
    temp = tempfile.NamedTemporaryFile().name
    image.save(temp,'tiff',**options)

We can also investigate how to use a command line pipe action with imagemagick (use - for pipes in command line).
With this action the sky is the limit. For example you could use it to integrate imagemagick and even Blender in Phatch. Not very efficient yet when you use them one after each other, but that doesn't matter yet in relation to the power it gives. Later we can optimize that.