CI: Improvement on python framework

CI improvements: the goal is to make CI framework more modular and debuggable/mantainable

The original main.py script was splitted into functional modules:

• sshconnection.py: handling connections between machines
• epc.py: handling EPC functions (initialization of nodes etc.)
• ran.py: handling all the e/gNB functions
• html.py: management of output data presentation
• helpreadme.py: a help on command line syntax is given when there are missing or wrong input parameters
• main.py: still contains the engine of the framework calling all the functions contained in the satellite .py files; and still contains all the functions pertaining to UE management (in a following step a dedicated ue.py dedicated file may be created)