Tune Nodes aspect

1. Put additional node handles on the side to avoid confusing input and output nodes (see bottom left node)
2. Tune CSS of nodes to be able to clean the aspect of the input/output nodes (this one is a bit messy sorry)

• Merge DataNode in Node (renamed RegularNode)
• Break down NodeContent in NodeWrapper and NodeTooltip: NoteNode needs the wrapper but not the tooltip
• Break down GraphInOutNode in InputNode and OutputNode. InputNode and OutputNode do not use the NodeWrapper since their aspect is different from the other nodes. This aspect was tuned according to one of our former discussion.
• Put all styling in Nodes.module.css. I could make one CSS module per node component but that seems overengineered. Node CSS rules now composes a common node class that gives the general node aspect.

There is probably some improvement to make so another pair of eyes is welcomed 😉