Silk4J API to expose OpenAgent file and directory operations used by 4Test

Since OpenAgent already supports the 4Test file and directory operation functions, it would be nice to have that functionality exposed via the Silk4J API. This would allow file and directory manipulation when running the tests on a different machine and connecting to the OpenAgent remotely.

The most important functions are:

SYS_FileExists
SYS_RemoveFile
SYS_DirExists
SYS_RemoveDir

This will allow the tests to clean up anything created by the application under test.

The ability to create files and directories and get their contents would be the next important functions. This would allow per-test files and directories to be created and the ability to get their content would allow verifying the correct changes were made by the application under test.

A Silk4J class modeled after the Java File class might be a nice way to implement this. That way the methods and signatures are familiar to Java programmers.