CB-11955 Added Initial OSX platform support

- Added src/osx plugin folder structure.
- Added OSX platform to plugin.xml and package.json files.
- Added _system target functionality for OSX.
- Modified README.md to include information about OSX support.
- Disabled 'open method' jasmine tests for OSX.

 This closes #190

README.md

@@ -69,7 +69,7 @@ Although `window.open` is in the global scope, InAppBrowser is not available unt
 Report issues with this plugin on the [Apache Cordova issue tracker](https://issues.apache.org/jira/issues/?jql=project%20%3D%20CB%20AND%20status%20in%20%28Open%2C%20%22In%20Progress%22%2C%20Reopened%29%20AND%20resolution%20%3D%20Unresolved%20AND%20component%20%3D%20%22Plugin%20InAppBrowser%22%20ORDER%20BY%20priority%20DESC%2C%20summary%20ASC%2C%20updatedDate%20DESC)
 
 
-## <a id="reference">Reference
+## <a id="reference">Reference</a>
 ## Installation
 
     cordova plugin add cordova-plugin-inappbrowser
@@ -145,6 +145,7 @@ instance, or the system browser.
 - BlackBerry 10
 - Firefox OS
 - iOS
+- OSX
 - Windows 8 and 8.1
 - Windows Phone 7 and 8
 - Browser
@@ -185,6 +186,12 @@ opened with `target='_blank'`. The rules might look like these
 }
 ```
 
+### OSX Quirks
+
+At the moment the only supported target in OSX is `_system`.
+
+`_blank` and `_self` targets are not yet implemented and are ignored silently. Pull requests and patches to get these to work are greatly appreciated.
+
 ### Windows Quirks
 
 Windows 8.0, 8.1 and Windows Phone 8.1 don't support remote urls to be opened in the Cordova WebView so remote urls are always showed in the system's web browser if opened with `target='_self'`.