This partially reverts cff8720a44, but keeps the
doc-string.
Rationale: TOPICs may contain notes which should be reviewd regularly. Those
TOPICs should also be tagged with NOTE but could (and should) in addition
contain sub-items about concrete tasks. In this case refiling to a NOTE should
be allowed.
Maybe limiting refiling to NOTE:TOPIC combinations would be more strict here,
but I think this complexity is not (yet) worth it.