management_df_from_excel: Import management_df from excel file
Description
This function imports management data from an excel template and
transforms it into a management_df.
Additionaly, it checks if all columns
that are expected for a managment_df are available.
The excel template can be found in the SoilManageR Package under
inst/extdata/SoilManageR_mgmt_data_template. Optionaly, the parameter
year can be overwritten by the year extracted from date.