[internal] Change names of connector attributes

[formatc1702]

The names of connectors' attributes will be changed to ease confusion.

• pinnumbers will be changed to pins
• pinout will be changed to pinlabels

Quoting an earlier discussion in #71:

• pins (previously known as pinnumbers) is the list of unique identifiers for each pin, and is autofilled with [1,2,...,<pincount>] when it not specified explicitly. It is useful for non-numerical pinout schemes like [tip,ring,sleeve], an alphanumerical matrix ([A1,A2,...B1,B2,...]) and others, and to manually reorder pin numbers if so desired ([4,1,3,2]).
• pinlabels (previously known as pinout) allows assigning labels to each pin, e.g. it's function (VCC, GND, ...). It is autofilled with ''and hidden if not specified.

This makes things more consistent by using plural words for lists (pins,pinlabels, a wire's colors, ...) [...]

• pinlabels do not have to be unique, but can only be used for defining connections if the ones being used are unambiguous