iOS : Add isFile and isDirectory support

This pull request addresses the below JIRA tickets.


JIRA Ticket [TIMOB-12414](https://jira.appcelerator.org/browse/TIMOB-12414)


JIRA Ticket [TIMOB-2181](https://jira.appcelerator.org/browse/TIMOB-2181)


Sample [app.js](https://gist.github.com/741829693f5644f67840) used in testing/verification