Esteemed maintainers,

I submit the following two patches to you for review.

They add breeze-assets and breeze packages.

Currently, guix only has `breeze-icons`, and this package only supplies the
icons, and not the entire breeze theme.

I have, however, a few concerns/comments regarding the patches.

# Regarding the first patch:
1. Regarding `breeze-assets`, I am not entirely sure if that is the right
name for the package. If there are any better suggestions, perhaps it
should be changed (?)
2. The `breeze-assets` package inheriting from `breeze-icons` package is
intentional: so as to show the relationship. I started with `guix
environment breeze-icons --ad-hoc stuffs` to package breeze-assets,
anyways. I think this makes it more read-able. (Can we keep it, please?)
3. I could not really find a proper home-page for the package.
4. I wonder if there should be better synopsis/description? But I'm not
sure. But if I get an 'it's all right', I'd like to run with it as-is,
please.

# Regarding the second patch:
1. I intentionally used (inherit, again, and used (@ to inherit from
mate.scm. Probably a bad idea. And it got me thinking, since union-builds
aren't all that common yet, perhaps a boilerplate union-build package could
be created. I saw that `mate` and `xfce` use almost identical package
definitions. Perhaps abstracting that away into some hidden package like
(@@ (guix some place) union-build-boilerplate) or something would keep us
from repeating ourselves? I understand that inheriting from something from
an entirely different desktop-environment might be too much spaghetti code.
And I am in favour of changing this. However, I send this patch in as a
sample of how having union-build boilerplate might help us.
2. I am not entirely certain what the version number should be. It seems
`breeze-icons` and `breeze-assets` differ in their latest version. But
since `breeze-assets` is the bigger of the two packages, I decided to go
with `breeze-assets`'s version number.

I hope to learn a lot from the review of these patches, and will try to
send updated/polished patches - as per the reviews - as promptly as
possible.

Thank you