json data import and legacy url redirection

Added optional support for loading data attributes to the imported pages through JSON encoded data. 

Added optional support for redirecting legacy urls for each imported item, using the redirected urls module.
 
 * fix: update existing pages on import, added delete redirects option on import
 * fix unit tests for json example
 * update readme url for static site connector module
 * updated readme maintainer details, help text and example file format