Add support for Adobe Air app installations

Adobe Air applications take the form of a .air file that the Adobe Air
runtime then installs and creates a .app -- typically in
/Applications.  This patch provides a new container for those .air
files which the Adobe Air runtime installs to the Caskroom.

Presently, if homebrew-cask doesn't detect the Adobe Air runtime, it
will provide an informative error message and instructions to obtain
it via `brew cask install adobe-air`.  This is obviously not ideal and
the installation process for the runtime should be automated in the
future.
Pandora One Desktop App

With the Pandora Desktop Application, you can play your Pandora
stations right from your desktop – without opening a new browser
window. Plus, because the desktop app is only available as part of
Pandora One, your music is completely free of all advertising.