[scripts] Fix of URL of Corine Land Cover database and add of year 2018 data

The notebook for creating a friction layer based on Corine Land Cover (CLC) was not functional anymore because of a problem on the URL of the Corine Land Cover database. While correcting this bug, I updated the function by adding data from more recent CLC zoning (2018) and made it as default. The def_strickler data for the notebook is renamed as it is not based on the year of the data, and should be modified by the user for using its own table coefficients.