#236 Replace "Create OpenPGP Rulke from Address" by "Edit OpenPGP rule from address" if there is already a rule

[Nicolai Josuttis]

On the mailing list we had the following conversation:

• When a rule is defined, replace the ability to define a
  recipient rule by the ability to EDIT the existent recipient
  rule. Thus, (at both places ) replace: "Create OpenPGP Rule
  from Address..." by "Edit OpenPGP Rule from Address..." starting
  the modify rule dialog with the current settings instead of from
  scratch. (If switching the menu entry is not appropriate rename
  it to "Create/Edit OpenPGP Rule from Address...".)

This works, if the per-recipient address is for exactly 1 email
address. But you cal also have rules like "ends with"
"@example.org", and rules with multiple email addresses. The menu
entry would therefore only edit an existing rule if the email
address matches exactly.

I see the point.
First, adding a new rule makes no sense in any case here. So this has
to change.

Depending on the effort I suggest something like:
- If there is an exact match,
start the rule editor for that exact match
(this is what novices will expect).
- If there is no exact match, you can:
- start the rule editor
- optionally with only the rule(s) that would match
- start the dialog with the rule that would currently apply
and IF there is a change in where the rule applies to
print a warning or add questions to ask whether to add
or replace the existing rule that covers a different group
of receivers.

Alternatively, as a simple approach:
- If there is a rule that already applies,
always start the rule editor instead.
That's probably the easiest and most intuitive solution
and better that just adding a new rule without the ability
to edit the existing rule without expert mode.