Add and Edit forms

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@Djordje

If there is a special occasion where one needs two forms (which is very rare) it is easier to add a new one from a copy of a single form.

While the UI of both forms might look identical in most cases there are significant differences:

1. Edit form needs parameter to populate fields, Add creates new instance and parameter is not needed.
2. Primary keys cannot be edited and are excluded explicitly from the Edit forms while in Add forms sometimes there are needed.
3. Selecting proper value in lookups is a must in Edit forms while in Add forms this is again not needed.
4. Add forms can be extended to handle built-in many-to-many relations while this is not needed for Edit forms.

I'm sure there are many other custom cases and so far, for 7 years our customers liked separate Add/Edit forms.