PATCH: pgAgent support - Mailing list pgadmin-hackers

Please find the patch for support for paAgent in pgAdmin 4.

I have also attached another patch for miscellaneous fixes, and adding new controls.

It includes:

- Added DatetimepickerControl, MomentCell (using moment.js)

- Used the 'DatetimepickerControl' in Role (Also - resolved an issue, when unset the datetime for 'Valid Until'.)

- Added a 'Select All/Unselect All' adaptor for Select2 used by pgAgent nodes.

- Fixed an issue with SubNodeCollectionControl, which was not starting the modification session of the child model, when created default value for collection is not null/undefined. And, hence - validation on the child model was not working.

- Fixed a memory leak with SqlFieldControl, and SqlTabControl, which was not releasing the CodeMirror properly.