Support file operations on non-textual files

[iliashkolyar]

Fixes #57 by supporting source path retrieval for non-textual files.

[iliashkolyar]

The bug was a failure to retrieve the source path of a non-textual file.
This failed not only the delete action, but basically every command that was triggered on this type of files.

Since I could not find any API that handles non-textual files (and thus could not get their source path), the solution was using the VS code copyPathOfActiveFile API and running some clipboard manipulations.

Unfortunately, due to this reason, I could not add a test for this scenario as I could not find a way of opening a non-textual file to begin with.
The following:

const uri = Uri.file(<path_to_binary_file>);
workspace.openTextDocument(uri);

Would return the following error: "cannot open <path_to_file>. Detail: File seems to be binary and cannot be opened as text", and I could not find any similar API for non-textual files.