Progress:

* dropdown menus modeled after gtk for GNU/Linux (ttk::combobox)

* native dropdown menus for Windows (ttk::combobox)

* native-ish dropdown menus for OSX (ttk::menubutton)

* multi-device button doesn't disappear when clicked (see attached audiodialog3.png)

* audio api/settings/devices all in a single window

* devices aligned in grid

* removed cruft: unnecessary colons, device checkbuttons, label repetition

* multi-device button disabled when there aren't multiple ins/outs

* single "connect" button to clarify when Pd is supposed to open audio

* can specify "None" as device (same as unchecking the device in the old audio dialog)

* replaced "Apply" and "Ok" buttons with "Connect", which is more explicit.  Also, it makes a nice flow from top to bottom: choose an api, the common audio settings, the specific devices (and device specific attributes: "channels"), and finally click "Connect".  Connect also saves the audio settings-- I think that's generally what the user wants to do, and there can be a more general feature to make "profiles" if the user has a more complex/dynamic setup.

I can also make it possible to specify no api (or a dummy one) if that's desirable.

Screenshots currently lack a "Close" button which will be common to all preference frames. (I.e., at the bottom of the dialog below the notebook widget.)

For my own sanity the API dropdown list currently shows Pd's api number as well as the API name.

-Jonathan