Correct dependencies in setup.py

Replace "dateutils" with "python-dateutil"
Fix incorrect error message in create server

Fixes #5
Quote the right part of the request URL
Restrict header encoding to specific headers

In ResponseManager, do not encode all headers to unicode.
Encode ONLY the headers mentioned by the caller method.

A caller method can use the headers_to_decode and header_prefices
property-getter/setter methods to set a list of header keys and
a list of header key prefices for encoding. All keys are case
insensitive.
Add lists of expected headers in Client classes
Handle console input/output encoding
Distinguish quoted from unquoted request headers

Introduce the "headers_to_quote" and "header_prefices" properties
in RequestManager class. Modify the class so that only matching
API-speicific header values are quoted before the request is
performed.

If an API-specific header is not explicitely declared quoted, its
value is decoded as utf-8.