Fix issue 11 - Add wordlist validation + dedupe

[jmiroosh]

Hi, The tools is very good, thanks!

I was getting some strange errors with bad wordlist entries, so I have added whitelist validation, for issue #11

Also added a test in system.py, but unsure how to verify that it passes. (!!)

Thanks

[null-hyp0thesis]

Actually, we could probably do with removing %/- and unicode chars from the wordlist too.

[nikitastupin]

was refactored in #66 thanks for you contribution again!