Switch gzip file type check from extension to "magic" bytes

[owlang]

GZipped an other binary formats have a specific sequence of bytes to mark the binary file type at the top of the file. We should be using this to determine file type rather than extension. A Java implementation of this check for both InputStream and File type objects is already written here.

[owlang]

Utilities for checking isGzip() has been created for updating current and future gzip tools