Add support for Adobe Air app installations

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.
Make SystemCommand escape arguments

Previously, SystemCommand executed shell commands in string form which
forced the caller to escape the command.  This patch changes this
behavior so that arguments are passed in a list and thus also escaping
the command properly.

The testing facilities required the most change as they require an
exact command -- escape characters and all.  It may be worth
revisiting in this in the future to allow for fuzzy matching of the
command strings to ease the writing of test cases.