Add a default submitter to newly created trees in order to enable a standard conform GEDCOM export

[Jefferson49]

In #4883, it was discussed that a new (default) tree in webtrees is created without a submitter. As a consequence, a newly created tree is exported with non standard GEDCOM, because the submitter is a mandatory object to be referenced in HEAD.

Maybe, it would make sense to generate a default submitter. It could have the same name like the default individual or the submitter name could be generated from the user data.

PROs:

• GEDCOM export complies to standard from the very beginning of a tree's creation.
• Users can get a hint about submitters (being mandatory) and might be triggered to add/complete it.

CONs:

• A generated default submitter might confuse the users; maybe, could be addressed by a note (like for the default individual).
• The default submitter might not be substitued by the users.
• Non compliance is not an important issue in this area.
• In GEDCOM 7, the submitter will not be mandatory; on the long run, it will not be an issue.

[Jefferson49]

Some further comments of @fisharebest from the discussion in #4883:

The submitter record could be empty - or it could contain the details of the user who created the tree.

We could also create a submitter record when importing a tree.

We could also prevent the final record from being deleted.

But I can think of one useability issue. Users would now see the submitter list in the menu - since they now have submitters in their tree.

For many users, submitters are fairly pointless. This "pointless" menu item will annoy people. Modules will be created to suppress it ;-)