Create settings widgets for some BQM tools only when they are needed.
Currently, at startup, all settings widget are created and kept in memory,
this should not be necessary.

A tool can choose not to create the widget in its constructor, but instead
implement a createSettingsWidget() method which must be called from
the framework before the tool is accessed. I hope to have found
all relevant paths where this must be done.

Not all tools are ported.