developed controllers for power-heat coupled network and plot it

[sf-snigdha]

developed controllers for power-heat coupled network and plot it

[EPrade]

Hey, cool that your idea resulted in this pull request. It is always a joy to welcome new contributers here!
The code looks good on the first glance. However the files could be sorted into seperate folders to fit the pandapipes structure. Maybe you can restructure the files and the we finalize this PR.

• the multinet controller would fit into the directory pandapipes/multinet/control
• the example/tutorial should be changed into a jupyter notebook and would then fit in the tutorial folder
• the plotting code can be moved to the plotting folder

Please ask if you have any questions.
Looking forward to more great contributions!