Oauth and better exception handling

Added support of the Tictail OAuth, so it's now possible to use the API
to optain an AccessToken based on a AuthCode (this is used when building
external tictail apps).
Added a TictailException for better handling of errors from the Tictail
API, with better messages.
Added additional unittests, espcially for the new OAuth and the
TictailException.
Updated readme

Rewrote the readme, with information how to use the OAuth.
Renamed the solution-file.
Updated AssemblyInfo
Updated readme

Create "what is this"- and "getting started" sections