Move towards `visu` Submodule

[engineerjoe440]

Many visualization functions can be grouped into the visu submodule, which, in itself should be structured to have submodules (I think bode should move there, eventually). A few of the functions that should be moved there include:

• Power Triangle plotter
• convbar convolution plot generator
• phasorplot Phasor diagram plotter
• bode plotting tools