Rework of the Wolfram Alpha fallback

[penrods]

This rework does several things:

• Added ability to request sources, generating an email to the user
• Removed "did you mean", which just gave interpretations you never meant :)
• Removed repetition of the question. It was awkward and stilted experience, at best.
• FIX: Changed normalization for special cases -- "how many inches in meter" wouldn't handle as well as "how many inches in a meter".
• Changed to Apache 2.0 licensing
• Switch the private API key storage to skill settings instead of mycroft.conf (with migration code)
• Switched to self.log instead of LOG
• Commented code!

[penrods]

@Mn0491 added .gitignore