Allow users to specify year and version of used data

[marcwie]

NUTS codes are updated every 4 years, LAU codes are updated every year. Currently the package parses NUTS codes for 2016 and LAU codes for 2019. Both are currently the most recent data sets.

In the future, users should be able to select a specific year through an optional parameter in the respective load functions.

In this case we also need to download the appropriate correspondence table.

Similarly, different version of the shapefiles exists which are labelled as 3035, 3857, and 4326 in the respective file names. Users should be able to select the appropriate version. For now the package always selects 4326.