Theme: initial integration of CSS for base WET Theme

- Partial cleanup up of base SCSS

- Changed dist/demo directory to dist/demos to align with existing v3.1 folder structure

- Now generating license files and update generated home files

- Updated build to move assets and plugin files to the new dist/demos directory

- Corrected duplication of accessiblity placeholders

- Removed sr-only trailing reference

Removed redundant accessiblity file