Replace CodeHarbourLink .erb wtih .slim templates

- this is consistent with the remaining view architecture

(leoselig/codeocean#2)

app/views/code_harbor_links/show.html.slim

@@ -0,0 +1,7 @@
+h1
+  = @code_harbor_link
+  = render('shared/edit_button', object: @code_harbor_link) if policy(@code_harbor_link).edit?
+
+- %w[oauth2token].each do |attribute|
+  = row(label: "code_harbor_link.#{attribute}") do
+    = content_tag(:input, nil, class: 'form-control', readonly: true, value: @code_harbor_link.send(attribute))