Utilities, script refactoring and search fix

Search now works as expected, even with multiple boards.
Scripts are now refactored, using argparse to parse scripts arguments. the "search" test works as expected too.
Added a new module, moesearch/utilities.py: it contains useful scripts for downloaders. more utilities will come, and new functionalities should be implemented there.

Everything is tested now: you may experience some errors in the unittests, but I can assure you it's unittest's fault: it signals exceptions I raise on purpose to apply different behaviours according to the "board" type, in moesearch.search function.