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
3 - merge with Rowan pull request
4 - fix an encoding issue when using the dry-run mode
5 - use getpass to hide the password when typing

I tested it (dry-mode and real mode) and it's works fine, but it's the first time I code in Python, so I hope that I didn't mess anything !