Add files for LinkBackSupport for Keynote 2

Final code for Keynote LinkBack plugin for Keynote 2. Originally
developed between February 2005 and March 2005.
Add files for LinkBackSupport for Keynote 3

Final code for Keynote LinkBack plugin for Keynote 3. Originally
developed February 2007.
Add files for LinkBackSupport for Keynote 4

Final code for Keynote LinkBack plugin for Keynote 4.
Fill in README file with info about the project

Describe the purpose of the project and its history. Also declare the
license to be Apache 2.