refactor!(*): use attributes that match projects

Previously we effectively had some projects smooshed together. This
normally worked fine but for any repeated attributes (e.g. default) both
copies would break.

Instead, we now have a new naming scheme:

Projects are given a "name" attribute in their config

# foo/project.nix:
{
config.name = "foo";
}

Any packages, shells, systems or homes defined in that project start
with that name followed by a dash

# foo/packages.nix:
{
config.packages.foo-package = {
...
};
config.packages.foo-package2 = {
...
};
}

# bar/packages.nix
{
config.packages.bar-package3 = {
...
};
}

Because of the naming convention, you'll still be able to refer to the
package even if another one is named the same

# baz/packages.nix
{
config.packages.baz-package2 = {
...
};
}

For the default package, the project name alone should be used for the
attribute

# foo/packages.nix:
{
config.packages.foo = {
...
};
}

To refer to a package elsewhere in the project, you must use the fully
qualified name

# foo/packageReference.nix:
{ config, ... }: {
config.something = [
config.packages.foo-package
config.packages.baz-package2
config.packages.foo
config.packages.package # fails - "package" does not exist
config.packages.default # fails - "default" does not exist
];
}

When using patisserie on the command line or from another project,
however, there are aliases for your convenience...

patisserie$ nilla build foo-package # works
patisserie$ nilla build package # also works

...but only if the package is unique

patisserie$ nilla build package2 # fails because there ore two packages called package2 (foo-package2 and baz-package2)
patisserie$ nilla build foo-package2 # still works
pasisserie$ nilla build baz-package2 # also still works

When using Josh to clone down part of the monorepo, only the current
project will be aliased, even if other pieces are included as
dependencies...

foo$ ls dependencies/
bar baz
foo$ nilla build foo-package # works
foo$ nilla build package # works
foo$ nilla build package2 # works - referring to foo-package2
foo$ nilla build bar-package2 # works - you can still use the full name of a package
foo$ nilla build package3 # fails - even though bar-package3 doesn't conflict, it isn't aliased in the foo project

...you may also use the default attribute to refer to the package with
the name of the cloned project...

foo$ nilla build foo # works
foo$ nilla build default # works
foo$ nilla build # works - since as nilla by default uses "default" if you don't specify an attribute