Unify connectors

[17o2]

Closes #78.

• Code has been adapted, all references to "ferrules" as separate connector type have been eliminated.
• The simplified look of a ferrule can be achieved by adding a style: simple attribute to a connector.
  • This simply eliminates the list of pins inside the node, and causes connected wires to attach to the node itself, rather than a subport
  • The simple style is only allowed for connectors with one [electrical] port:
    • ferrules
    • splices (may be two-way, three-way or more)
    • Wagos / Wire nuts (see [feature] Support for Wago connectors #45)
• The auto-generation of simple connectors is achieved by the autogenerate: true attribute
• Autogenerated connectors hide their (also autogenerated) name by default, and their designators are not listed in the respective BOM column
• Some examples have been updated/simplified to work with these changes

[kvid]

IMHO, the more compact code versions are not less readable.

[kvid]

I really like the more compact way to specify connections in the YAML file.