Android: Update "Ti.Filesystem.File" to support exists(), extension(), and read() when wrapping "content://" URL

Summary:
When passing an Android "content://" URL to the Ti.Filesystem.getFile() method, the returned File object does not support the following methods. They will return failure results and log a "Method is not supported" warning.

• File.exists()
• File.extension()
• File.read()

We should add the above methods for consistency.

Note:
The File object already correctly implements all other methods and properties for a "content://" URL such as the copy() method and "nativePath" property. Adding the above methods will help make the interface more complete and avoid confusion.

Implementation:
We need to add the above methods to our TitaniumBlob Java class.
https://github.com/appcelerator/titanium_mobile/blob/master/android/titanium/src/java/org/appcelerator/titanium/io/TitaniumBlob.java

We can test the inclusion of these methods with the attached FileContentUrlTest.js file. This test script assumes its was created via a Classic Default project template.