Add an IFile::queryCapabilities()

It needs more thought, but the plan is for this to solve a variety of configuration issues.  It would return information about the kind of file that is being used to implement an IFile

const FileCapabilities & IFile::queryCapabilities();
class FileCapabilities
{
public:
    size32_t minBlockSize;
    size32_t maxBlockSize;
    size32_t recommendedBlockSize;
    bool     hasDirectories;
    bool     canRename;
    bool     canSeek;
    bool     canAppend;
//etc
}

It would hopefully allow us to cleanly parameterise the difference between local and remote file systems, and the different cloud providers.