Make members protected if accessor methods are being used

Accessor methods are generally used instead of (not 'in addition to') direct variable access.  wsdl2phpgenerator currently creates classes where both the variables and the accessor methods are `public`, which makes for a redundant and confusing API.

Well-written classes should only allow getting/setting via one of the two approaches.  If a user of wsdl2phpgenerator wishes to use accessor methods, we should make the variables protected so that only accessor methods can be used.