Query Cu-fcc surface energies from atomsitictools.org

Add Jupyterbook

Update potential database 

add df4 to day2/00-IntroductionDay2.ipynb

# Conflicts:
#	day_2/00-IntroductionDay2.ipynb

Executed all the notebooks again on workshop.pyiron.org

# Conflicts:
#	day_1/ex_01_introduction_to_pyiron.ipynb
#	day_1/ex_02_creating_structure_databases.ipynb

Cosmetic changes

Clean up day3

Runner use central dataset

Pacemaker - remove pyiron_gpl from requirements

Place database inside resources 

Final changes: All types of potentials are now included in the validation notebooks! Hope this works!