Don't print "could not find" warning for attributes defined in a scannerSettings template

[han16nah]

When using a scannerSettings template (see Wiki - Scanner settings) to define the scanner attributes of a <leg>, warnings about missing attribute values are printed, even though they are defined in the template, e.g.:

XML Assets Loader: Could not find attribute 'pulseFreq_hz' of <scannerSettings> element in line 49
Using default value for attribute 'pulseFreq_hz' : 1000000

It seems like for the warning, it is only checked if an attribute value was defined in the <scannerSettings> tag of the leg but not if it is defined using a scannerSettings template. For the user, this leads to confusion about whether or not an attribute value is correctly set.

Task: Adapt the warning/error message, so that there only is a "Could not find, Using default value" message if no attribute value was found in either the defined scannerSettings template or directly in the scannerSettings of the leg.

[han16nah]

fixed with #142