Sub-Task Region Improvement

Subtask Brower and Add Eubtask Region is Very usefull to our JIRA implementation
but we need some improvements on this feature, here they are:

• Add Field(s) default or Custom and set them not nullable on Add Sub-task
• Use this Add Sub-task region as default Sub-task addng feature (currently this feature only available when a task already has subtask)
• Add Column Header with sorting capability on Sub-task browser
• Configurable columns on Sub-task browser