Remove leading and trailing white spaces in columns names

        :example: ``ds.strip_cols()``

def strip_cols(self):
        """
        Remove leading and trailing white spaces in columns names

        :example: ``ds.strip_cols()``
        """
        cols = {}
        skipped = []
        for col in self.df.columns.values:
            try:
                cols[col] = col.strip()
            except Exception:
                skipped.append(str(col))
        self.df = self.df.rename(columns=cols)
        self.ok("White spaces removed in columns names")
        if len(skipped) > 0:
            self.info("Skipped columns", ','.join(
                skipped), "while removing white spaces")