simplify sequence export from GDE interface (treeing-tools)

[westram]

Motivation:

Treeing tools called via GDE basically perform 3 different actions:

1. build a new
2. calculate something with existing (e.g. -optimize/-evaluate)
3. add extra species into existing

The sequences of the following species have to be exported in these cases:

1. marked or all
2. all species that are members of the
   ⇒ has to unmark all species + mark all species in tree
3. same as 2. plus all extra species
   ⇒ has to mark only extra species + mark all species in tree

Wanted behavior:

1. leave as is (=export marked or all)
2. ignore species marks and always export species which are members of selected
3. export marked plus members of selected

Providing that behavior has some implications:

• selection has to become a global option (like marked/all- or alignment-selection)
• marked/all-selection has to be expanded with two new options: treemembers, marked+treemembers
• (de-)selecting a could toggle between
  • marked ↔ marked+treemembers
  • all ↔ treemembers

Some error cases could/should be checked by GDE interface:

• no selected AND treemembers exported
• overlap between marked and treemembers (only warn?)
• …?

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Related: #681