Implement check to avoid starting a simulation with unconnected components

[josihoppe]

added js check to see if the nodes are connected before saving

Since I solved this on the client Side the nodes don't know what kind of type they are and I needed to base the validation of of their names. Right now I have implemented the validation with this logic:

• name that starts with "bus": need to have at least 1 input and 1 output
• name that ends with "demand": need to have at least 1 input
• the rest (which I think are mostly sources): need to have at least

I am not sure if like Conversion nodes need to be handled differently, but more diverse checks could be implemented.

[paulapreuss]

I noticed that for components with in- and outputs it only checks for outputs (it will still save if the component has only an input set). This also applies to buses, although those even have an explicit check condition, I think the condition might not be called properly.

The most important check though is that no component gets lost without any connections, and that seems to be working fine :)