Make a carp_themes_package

[Panosfunk]

Since most of our packages that have some ui aspect to them, use the same themes/colors/assets, I suggest we create a new package called carp_themes_package that incorporates all of those ui elements and is just called wherever it's needed (studies_app, research_package). Even though there are not that many packages that use those UI elements, I think its good practice for scalability reasons.

Thoughts? @iarata @bardram

[bardram]

Sounds like a good idea - let's do that.

We can make it an unlisted package at pub.dev