Select cell under cursor
        cell = group of lines separated by CELL_SEPARATORS
        returns the textCursor and a boolean indicating if the
        entire file is selected

def select_current_cell(self):
        """Select cell under cursor
        cell = group of lines separated by CELL_SEPARATORS
        returns the textCursor and a boolean indicating if the
        entire file is selected"""
        cursor = self.textCursor()
        cursor.movePosition(QTextCursor.StartOfBlock)
        cur_pos = prev_pos = cursor.position()

        # Moving to the next line that is not a separator, if we are
        # exactly at one of them
        while self.is_cell_separator(cursor):
            cursor.movePosition(QTextCursor.NextBlock)
            prev_pos = cur_pos
            cur_pos = cursor.position()
            if cur_pos == prev_pos:
                return cursor, False
        prev_pos = cur_pos
        # If not, move backwards to find the previous separator
        while not self.is_cell_separator(cursor):
            cursor.movePosition(QTextCursor.PreviousBlock)
            prev_pos = cur_pos
            cur_pos = cursor.position()
            if cur_pos == prev_pos:
                if self.is_cell_separator(cursor):
                    return cursor, False
                else:
                    break
        cursor.setPosition(prev_pos)
        cell_at_file_start = cursor.atStart()
        # Once we find it (or reach the beginning of the file)
        # move to the next separator (or the end of the file)
        # so we can grab the cell contents
        while not self.is_cell_separator(cursor):
            cursor.movePosition(QTextCursor.NextBlock,
                                QTextCursor.KeepAnchor)
            cur_pos = cursor.position()
            if cur_pos == prev_pos:
                cursor.movePosition(QTextCursor.EndOfBlock,
                                    QTextCursor.KeepAnchor)
                break
            prev_pos = cur_pos
        cell_at_file_end = cursor.atEnd()
        return cursor, cell_at_file_start and cell_at_file_end