Session handling class

This week I worked on class responsible for managing UI and class used to connect UI with the world. After talking with Remko I transformed WhiteboardController into WhiteboardManager because there is no need for typical controller but only for something taking care of WhiteboardWindow instances. Receiving and sending of data in WhiteboardWindows is done  through WhiteboardSession. Work on this and session manager classes took me most of the week. It can now send and receive raw data and initialize session with other user. Session initialization from user side looks very similar to initialization of file transfer. On received session request information about it with option to accept or cancel session is added to chat window.