create single scss pack and script

remove unnecessary file from pack
fix problem dev change style
fix theme picker

demo-shell/src/styles.scss

@@ -1,5 +1,5 @@
 @import '~@angular/material/theming';
-@import './custom-style.scss';
+@import '~@alfresco/adf-core/theming';
 
 body, html {
     margin: 0;