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.