Better support for shunt data and transformer ratio (voltage)

[BDonnot]

Shunts

With two modes, one being "continuous variable" which is like today, where a shunt can absorb / produce as much reactive power as it wants.

And a "discrete" mode, with a description file for example, that details the different taps you can have.

The choice between the two would be a parameters of the env.

Also make it easier to set shunt data and bus (using the properties of the action for example). Be careful it should be either a continuous variable or a discrete one.

Transformer

Same as shunt : continuous mode where you can modify the transformer ratio as much as you want. And discrete mode where you have some taps.

A description file to describe that.

And also a way to set these in the action