Add url encoding of the email

 - Extend API und Request class with a parameter 'encode_email', default to False
 - If encode_email is True, the email input is html encoded (urllib.quote)

cloud&heat are using a concatenation of <tenant_id>:<email> to identify the user.
This way of concatenating is typical for OpenStack installations. To still use
this string for authentication this needs to be encoded, but would break existing
cloudControl installations.
Merge pull request #5 from cloudControl/encodeemail

Add url encoding of the email