Fix for issue #791. Choose which fields to show in table panel details view

You can now set which fields you want to be visible in the details part of the table panel.

Added the option in the editor to set which fields you want to see.

Added an array `visible_fields` to keep track of the fields. 

Added a filter `visibleField` for showing the fields in the details view of a record. When the array is empty all fields are shown by default.