Added stubs for "Max adapter" classes.

These classes will process Responses received by MaxPeers, and then
decide what outlet they should go out, and whether they require any
preprocessing to account for the various legacy quirks of Max objects.

For example, an [rslider] object with a nominal range of -1:1 will
output values in that range. However, to set the values of that same
object one must give it values in the range of 0:2!

Similarly, the [umenu] object, used by AttributeServer clients with
Option/Push/Pull/Datatypes, requires a bit of setup before it becomes
useful. That setup would best be handled automatically by the
Java-backend, rather than bogging down Max patches with menu-building
code.