Encoding and import filter

1 - Allow to fix unicode issues with foreign language
2 - add a -f option which allow the user to specify a bitbucket issue ID to start import. Useful in case where the import crash in the middle of the processing (like an encoding issue), or if the user don't want to import all the issues

I tested it and it's works fine, but it's the first time I code in Python, so I hope that I didn't mess anything !