Merge pull request #61 from apmuthu/master

Merge from AP pull#63 - re structure.sql ordering, json data id dupe fix
issue 55 fix
Merge pull request #62 from apmuthu/master

Removed Product Matrix Extension as it is now part of the core
Merge pull request #4 from simpleinvoices/master

Merged issue #55 fix from simpleinvoices/simpleinvoices