I've been using doom-themes' doom-vibrant for long enough now that I'm
certain I won't be moving away from it anytime soon. So let's simplify
and strip away all other theme setup stuff.
The core setup files for Emacs Siren which lives in the core directory
followed a `siren-*.el` naming convention, which is the same as the
naming convention for modules.
This means that the `modules/core/siren-packages.el` module for adding
packages for Emacs package development, was not being loaded due to it's
name conflicting with `core/siren-packages.el` which sets up and
configures the packaging system.
So all files under the root `core` directory now follow a
`siren-core-*.el` naming scheme, meaning modules should no longer
conflict with core files.
