Minor adjustments to handling read-only files

Currently CH by default protects read-only files (i.e. not deletes nor overwrites them).
The proper way to handle such files would be to ask user to decide what to do with such files. There is no such option at this point and it is planned for the future release.
In an attempt to make CH a little easier to use, implement the following:
1. Change the default setting of "Protect read-only files" to false. That way it will be coherent with the Window's (8.1) copying works (it just overwrites the file without asking).
2. Fine-tune the code that changes the attributes (disables read-only attr) to be executed only when we know that we're dealing with read-only attribute (and in case it is not known yet, it needs to be confirmed when the original request fails with access denied error).