Enhancement (coding style)

This PR contains some coding style improvements.

I would recommend 
* to use argparse instead of a manual parsing.
* to move .mga3prepo in .config (which is more standard)
* to move the data in print statements in info() to a config file (ini or json). We can imagine an online json file, allowing update without new packages.

I fixed only the msot obvious things, but there is probably much more to do. I thought to similar tools I was on mandriva :)

Please, double check my modifications before merging.