Update original course to this new one day course on functions and modules

[pajanne]

Possibles sessions:

• session1 : python basic - datatypes and collections, conditions, loops and files + a recap exercise
• session2 : functions - writing reusable code within your own script (old day2_session1)
• session3 : modules - writing reusable library and using existing ones os, csv (old day2_session2&3)
• session4: using external libraries - biopython (old day2_session4) and maybe another one