Adding Adobe Photoshop CS6 (#1830)

Installed using this script and verified success.
Uninstallation works via dynamic creation of uninstallation script
from an installation one. Verified to work.

Casks/adobe-photoshop-cs6.rb

@@ -0,0 +1,37 @@
+cask 'adobe-photoshop-cs6' do
+  version '13.0'
+  sha256 'f377a661660a5b00c46ef71dd5a835989d1374ed97bb891e9bdf98fa3a686a5e'
+
+  # This Cask entirely based on @winkelsdorf's epic CS6 cask checkin:
+  # https://github.com/caskroom/homebrew-versions/commit/d0255946a4d1bc1f553461f9e0143459964caf6d
+
+  url 'http://trials2.adobe.com/AdobeProducts/PHSP/13/osx10/Photoshop_13_LS16.dmg',
+      user_agent: :fake,
+      cookies:    { 'MM_TRIALS' => '1234' }
+  name 'Adobe Photoshop CS6' # name must match directory in dmg for later reference
+  homepage 'https://helpx.adobe.com/x-productkb/policy-pricing/cs6-product-downloads.html'
+  license :commercial
+
+  installer script: "#{staged_path}/#{name.join}/Install.app/Contents/MacOS/Install",
+            args:   ['--mode=silent', "--deploymentFile=#{staged_path}/#{name.join}/Deployment/en_US_Deployment.xml"]
+
+  preflight do
+    system '/usr/bin/killall', '-kill', 'SafariNotificationAgent'
+  end
+
+  uninstall_preflight do
+    uninstall_filepath = "#{staged_path}/#{@cask.name.join}/Deployment"
+
+    uninstall_file = File.open("#{uninstall_filepath}/en_US_Uninstall.xml", File::WRONLY | File::TRUNC | File::CREAT)
+    uninstall_file.write(File.read("#{uninstall_filepath}/en_US_Deployment.xml").gsub(%r{install}, 'remove'))
+    uninstall_file.close
+  end
+
+  uninstall signal: [%w[KILL SafariNotificationAgent]],
+            script: {
+                      executable: "#{name.join}/Install.app/Contents/MacOS/Install",
+                      args:       ['--mode=silent', "--deploymentFile=#{staged_path}/#{name.join}/Deployment/en_US_Uninstall.xml"],
+                    }
+
+  caveats 'Installation or Uninstallation may fail with Exit Code 19 (Conflicting Processes running) if Browsers, Safari Notification Service or SIMBL Services (e.g. Flashlight) are running or Adobe Creative Cloud or any other Adobe Products are already installed. See Logs in /Library/Logs/Adobe/Installers if Installation or Uninstallation fails, to identifify the conflicting processes.'
+end