use string.Concat(x) instead of string.Join("", x)
fix custom smiley support
ChatboxConnector: fix editing messages
dispose of MemoryStreams
DOM: change text node inheritance

SmileyTextNode used to inherit from TextNode; now both inherit from
a new abstract class NodeWithText. This structure makes it easier to
clarify intent during type checks.
more tests
HttpInterface: it's working!