Change date/time format to ISO8601 on JSON serialization

This is my approach to issue #544 to provide support to ISO8601 standart on JSON serialization.

The ISO8601 is fully supported only by SimpleDateFormat in a JDK 7 and JodaTime. 
To support 100% ISO8601 specs and maintaining compatibility to JDK 1.5 compliant, the solution was to use convertion by regexp rules.

This solution can impact in existing code, and needs to be analyzed.