Tweak "Compare taxonomy"

[westram]

• add new mark-modes:

"mark only"	mark target species, unmark rest
"mark all but"	mark target species, unmark rest
"don't touch"	do not change any marks

• add toggle "Delete from rest?" to "Write level-change to field"
• add "Show?" toggles to selection lists:
  • one one may be checked
  • if checked ⇒ set -awar of 1st -canvas (=show )

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related: #654, #444