Add support for Adobe Air app container

Adobe Air applications are packaged in .air files which are then
installed by the Adobe Air runtime on a user's system.  Typically, the
installed file takes the form of a .app which can then be treated like
any other application bundle.  This patch adds support for a new .air
container format.  The name of the installed .app should be provided as
a link artifact in the cask.

Presently, if homebrew-cask doesn't detect the Adobe Air runtime during
installation, it will provide an informative error message and
instructions to obtain the runtime via `brew cask install adobe-air`.
This is obviously not ideal and the installation process for the runtime
should be automated in the future.