Attributes added to work item presentations which do not exist in work items created prior to the attribute being added should not be visible in the web browser and be consistent with Eclipse presentation

This is useful to allow new attributes to be added to work items which will be used for newly created work items, without causing confusing unpopulated information to be presented in existing work items in the web browser which do not contain that information, and which should not and do not need to contain that information because they were resolved prior to the addition of the new attributes.

Currently in Eclipse, when new attributes are added to a work item and added to the editor presentation, those attributes are only presented in work items which contain those attributes, this is newly created work items and any existing work items which have been specifically updated to include those attributes. For any pre-existing work items created prior to the addition of the new attribute and which have not had the attribute added, the attributes are not presented. This is a useful and clear and means that attributes which do not exist in the work items are not presented as uninitialised data which causes confusing when people view those work items. It is also clear in reports, because new attributes which are included in a report are shown as "not applicable".

However in the web browser, the new attributes are presented as data in it's "unpopulated" form, this causes confusion, because there can potentially be thousands of existing resolved work items without that data, which was not needed when those work items completed their workflow but is only needed for newly created work items. Reporting that data causes confusion when those existing work items are retrospectively opened in the web browser because it looks as though there is unpopulated data.

As existing work items can be updated to include new attributes, there is already a method to allow those attributes to be presented for existing work items if desired, by adding them to the work item, however currently with the web client there is not a method to prevent those attributes from being presented. A work around exists, by "hiding" attributes which do not exist in the presentation, but those add complexity and have risk that if a user selects the "uninitialized" value, the attribute will disappear from the presentation completely even for new work items - probably there are ways to protect against that with advanced advisors, but those add further complexity.

It would be be better if the Web Client was consistent with the Eclipse client which does not present work item attributes in work items which do not contain them, this allows the full choice, when adding new work item attributes, to either:
- only present the new attributes for new work items
- present the new attributes in existing work items by adding the attributes to them
- not present the new attributes in existing work items by not adding the attributes to them

The web client does not support the last option, this is only supported in Eclipse.