Add Pandas object (datatype) support to NOMAD

Currently, NOMAD supports python base variable types such as int, float, str, etc. and numpy arrays.

A lot of upcoming data is expected to be columnar, and pandas is one of the standard libraries that is used to treat such data. NOMAD is also using the pints python package to keep track of units in scientific data.

The pints library has an extension available for the pandas library called pint_pandas. It adds a parameter "unit" to pandas Series. Operations involving different columns also behave as expected, such as multiplication between two quantities and throwing an error if two quantities with unmatched units are being added or subtracted. The examples can be seen on the documentation page of [pint_pandas](https://pint.readthedocs.io/en/stable/pint-pandas.html).