Unnecessary subtitleData.data copying

[mgoral]

We don't need to copy (clone) it all the time. For instance, whenever ChangeData command isn't executed, it's probably not a place for a whole copy. Example from SubtitleTabs.py:

def _updateFile(self, filePath):
    items = self.__fileList.findItems(filePath, Qt.MatchExactly)
    if len(items) > 0:
        data = self._subtitleData.data(filePath)
        for item in items:
            item.setText(1, data.inputEncoding)
            item.setText(2, data.outputEncoding)
            item.setText(3, data.outputFormat.NAME)
            item.setText(4, str(data.fps))

            videoIcon = QIcon(":/img/film.png") if data.videoPath is not None else QIcon()
            item.setIcon(4, videoIcon)

We don't even use subtitles here. Instead, we could introduce e.g. non-copying accessors in DataModel for encodings, fps and things like that.

OR EVEN BETTER: make subtitles copy-on-write (copy-on-edit, frankly).

[mgoral]

There are many, many stupid, unnecessary, counter-intuitive copies. Like in SubManager:

    def __getitem__(self, key):
        return self._subs[key].clone()

    def __iter__(self):
        for sub in self._subs:
            yield sub.clone()

They should be checked and possibly removed.