ENH - put toolbox extraparameter handling in specific classes #311

Currently, in aas_inittoolbox there is a parsing of toolbox extraparameters. This assumes that the extraparameters for different toolboxes can be handled the same, whereas this is something that is actually quite specific for a particular toolbox. I.e. that if there are colons in the value, then that value should be split.

Since the extraparameters are specific for a particular toolbox, it makes more sense to put the handling of these parameters as a static method in the specific toolbox class. That also makes it more clear which toolboxes have known extraparameters.

The toolboxClass they all derive from would define a do-nothing default method, or even no method at all, since the method will only be called for classes that expect extraparameters.

In aas_inittoolbox it could then look something like

        params = {};
        if isfield(TBX,'extraparameters') && ~isempty(TBX.extraparameters)
            parse_extra = str2func([tbxname 'Class.parseExtraParameters']);
            params = parse_extra(TBX.extraparameters);
        end

        constr = str2func([tbxname 'Class']); 
        T = constr(TBX.dir,params{:});