This changes they was settings (what the user provides) are handled.
Before this, settings were passed as an object and that was it.
Now, settings are treated as an array of settings objects and this adds
full support for managing multiple sets of settings in a single pattern
instance.
This is the mechanism that's used for FreeSewing's sampling which used
to be a rather hackish implementation, but now merely sets up the
relevant list of settings, and then calls `pattern.draft()` as usual.
Things to be mindful of is that parts, the store and settings themselves
are tied to each set of settings. So where they used to be an object,
they are now an array of object.
This moves resolving of the config from the pattern constructor to the
init() method. The idea is that adding a part to a pattern is exactly
the same as adding a part to a design. In other words, late-stage adding
of parts would be no different as the config gets resolved after that.
This is currently broken in many different ways, but the unit tests
particular to this new way of resolving the config do pass.
