First stab at hosting Launcher's help content on a remote server.

I thought wx.html.HtmlHelpController's AddBook method was
supposed to be able to accept a zip file, but I couldn't
get that to work on Mac OS X (not sure about other OS's),
so I am unzipping the ZIP archive to a temp directory.

Haven't implemented clean-up yet, i.e. multiple runs of
the Launcher could result in multiple copies of its help
files being stored on the user's local machine.