Control center design

[jinningwang]

To further enhance manipulating the simulation, I suggest developing a "control center". It can handle the necessary manipulations in a more organized way, such as device connectivity, AGC response, randomness in generation, or changing load level. We welcome your input to help us better understand the potential usage of ANDES.

Three types of functionalities I can imagine now:

1. Device connectivity manipulation. Instead of adding a Toggle, an API can be developed to allow more easier manipulation.
2. Timeseries simulation. It achieves generation and load fluctuation by setting the according devices' reference, where the timeseries data is loaded from a timeseries file (maybe in CSV format).
3. AGC control. This one might require a link table to handle the necessary calculation: https://ltb.readthedocs.io/projects/ams/en/latest/_examples/demo/demo_AGC.html#ANDES-settings

Potential implementation:
Develop a class ControlCenter, and set it as a system attribute as System.cc.
It takes input of timeseries data. it has a method trip to manipulate device connectivity.

It is motivated from following discussions: #524, #496, #477