Standardize corners, backgrounds, and borders (#2271)

* Create shared ruler view

* Use collection rendering/spacer templates for rules, and new shared_ruler

* Use shared ruler for all the places a ruler is used

* Use shared ruler for imports and balance sheet

* Fix brakeman by using a static partial with a defined collection

* Standardize & improve a bunch of corners, fix some backgrounds, fix merchants for dark mode

* Update balance sheet

* misc cleanup

* Fix import table

* Remove middot

app/views/accounts/index/_account_groups.erb

@@ -11,7 +11,7 @@
         <p class="ml-auto"><%= totals_by_currency(collection: accounts, money_method: :balance_money) %></p>
       <% end %>
     </div>
-    <div class="bg-container rounded-md">
+    <div class="bg-container rounded-lg shadow-border-xs">
       <% accounts.each do |account| %>
         <%= render account %>
       <% end %>