Deprecated Frame.append from pandas

[Fahdben]

Since the version 1.4.0 of pandas the DataFrame.append is deprecated and should be replaced by pandas.concat.

The function build_reference_geom is still using the DataFrame.append method.

One way of solving this isssue is by replacing:

 output = output.append(tile)

with

 output = pd.concat([output, tile], ignore_index=True)

Thanks!