Added socket timeout to HTTPSConnection

Without the timeout, disqus-python can hang on a slow connection or slow API. If not set, the global default timeout setting is used, which can also be set with `socket.setdefaulttimeout(30)` (which is how we got around the `SSLError: The read operation timed out` exception thrown on slow internet days)

Added tests for the setter, but there are no tests for what happens when the connection is bad, which is probably why this particular issue was never noticed.