Resolve WB-475 - Allow medial wall to be filled while other label entries are...

Resolve WB-475 - Allow medial wall to be filled while other label entries are outline.  GiftiLabel was changed so that a function is always used to set the name of a label.  In this function, the label's name is examined to determine if the name is a medial wall name (name contains the text "medial" followed by zero or more characters, followed by "wall").  If it is a medial wall name, a flag is set and the flag can be queried.