app/views/products/show.html.erb: Bach to prev.
app/views/brands/show.html.erb: Back to prev.
Remove Back link from show page of brand and product.
app/views/layout/application.html.erb: Add link to dashboard if user signed in.
app/views/products/show.html.erb: Update.
app/views/products/_form.html.erb: Dsiable edit slug.
At edit page of brand and product, Back link to dashboard.