Add support for "inverse" groups

[westram]

When setting the root of the to the marked subtree shown here the resulting looks like this

Problem:

The semantics of the groups Archaea and Euryarchaeota did change, e.g. Archaea now contains Bacteria.

Proposed solution: use inverse groups

• change name of SomeGroup into !SomeGroup for all groups between old and new root
  (!SomeGroup should be interpreted as inverse of SomeGroup, i.e. as not SomeGroup).

In the example shown above, that means Bacteria is part of 'not Archaea' which is true. In fact the position of 'not Archaea' would need to be placed at the same node as 'Bacteria' (because 'Crenarchaeota' is part of 'Archaea'!), but this would cause too many problems and make things too complicated!

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required by: #449, #451, #512
related: #753

[westram]

by [17110]

[westram]

See help describing ​implemented solution