Vastly updated theme, settings and functions files to complete a working pass model of the layout builder.

Updated libraries file to pull correct default CSS file for Omega after refactor of SCSS/CSS generation

Adding in $theme.layouts.yml which defines the layouts available and also adding in 3 default (mostly identical) layouts to install to $theme.layout.$layout_id in the config table

Cleanup of omega.settings.yml to avoid storing any (or too many) layout arrays in there, causing the file to be unwieldy

Adding theme settings file to handle the layout configuration, or selecting a configured layout for various page types. Needs to be completed for functionality match with 7.x-5.x

Adding in region_classes to region containers to signify .with--content .with--sidebar-first .without--sidbar-second, etc.

Update to default mobile_portrait breakpoint to be all inclusive UP TO the mobile_landscape breakpoint.

Update to use base_path() instead of $base_path in layout compiling functionality when determining path location

adding function omega_return_active_layout() from 7.x-5.x with some functionality commented out for now

Vast rewrite of theme, theme-settings and omega.js to bring back most functionality that was present in 8.x-5.x-alpha1. This does not entirely fix all issues, but brings pre-release version back to near working order.

Removing breakpoint group and individual breakpoint .yml files per D8 changes to breakpoint implementations

Updating libraries and setting style theme settings to enable/disable entire library, not just css file.

git commit -m 'Issue #2424783 by purencool, dcmul: list_themes function does not exist' --author="dmulindwa <dmulindwa@2505784.no-reply.drupal.org>"