ENH: Added new multiRegion function object

Wrapper that clones the supplied object for each region.

Simplifies the setup of identical post-processing requirements for
multi-region cases.
Applies the supplied function to all regions by default.

Example of function object specification:

    multiRegion
    {
        type    multiRegion;
        libs    (utilityFunctionObjects);
        ...

        function
        {
            // Actual object specification
            type    fieldMinMax;
            libs    (fieldFunctionObjects);
            fields  (<field1> .. <fieldN>);
        }

        // Optional entries
        regions     (region1 region2);
    }

    Where the entries comprise:
        Property   | Description                    | Reqd | Default
        type       | Type name: multiRegion         | yes |
        function   | Function object sub-dictionary | yes |
        regions    | List of region names           | no  | all