This fixes some bugs in contact editing:
- a changed address is now checked for validity. Shows
error if invalid and restores prior value
- the changes are saved, before they were dropped
- adding a new contact switches to the contacts tab,
it used to switch to the address tab
As an enhancement, the contact name, as well as its address,
can be edited and updated.
Finally, the platform edit key can also be used to edit,
in adition to double-clicking. This is typically the F2 key.
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