#718 - Fixed few defects in task extension

task config properties are ordered based on display-order by default. If not set, the properties will be ordered based on the order they appear in the config
For Api-based plugins default value for required field is set to false, and the flag is set to true for Json-based plugins
provided display-name, display-order and required fields in sample curl plugin
#718 - fixed failing test
Merge pull request #773 from jyotisingh/task_extension_config_order_defect

Task extension config order defect