Changes on generic pv system

[k-rieck]

• some changes on generic_pv_system.py
• so far two calculation methods:

1. simphotovoltaicfast (the one that was used so far, seems to have errors and ignores module and inverter data)
2. simphotovoltaic_two (uses module and inverter data from database but apparently pvlib can only handle sandia modules)

the results of both methods seem similar although method 2. produces slightly less electricity: -> method 2.- kpi production full year = 17602 kWh vs method 1.- kpi production full year = 18092 kWh -> maybe more checks are needed -> the link to the full year results will follow

• right now this branch uses still method 1.
• with method 1. (as no module and inverter data is read from the database) also more efficient cec modules as shown in the test "test_generic_pv_system_fast_with_two_different_models.py" can be used

[k-rieck]

link for full year simulaion results : https://drive.google.com/drive/folders/17EZjwnt50FTwznuvwrG0LCUdkSUVtzki?usp=drive_link