Modifier doesn't handle string parameter values correctly

[Trevor Hardy]

GridLAB-D parameter value that are strings can either be quoted or not quoted and be correctly parsed by GridLAB-D. The GLM Modifier directly captures the string (including quotes if present) and provides this to users as the parameter value. As a convenience to the user, it would be helpful if the Modifier understood that the quotes were not part of the string itself. If the user modified that string parameter, when the new .glm is written out the quotes were around the new, modified, entire parameter name.