Basic donation records

Adds donation model/table and basic manual management in the admin
panel, as well as basic listing of users' own donations.

app/views/admin/donations/show.html.erb

@@ -0,0 +1,29 @@
+<p id="notice"><%= notice %></p>
+
+<p>
+  <strong>User:</strong>
+  <%= @donation.user_id %>
+</p>
+
+<p>
+  <strong>Amount sats:</strong>
+  <%= @donation.amount_sats %>
+</p>
+
+<p>
+  <strong>Amount eur:</strong>
+  <%= @donation.amount_eur %>
+</p>
+
+<p>
+  <strong>Amount usd:</strong>
+  <%= @donation.amount_usd %>
+</p>
+
+<p>
+  <strong>Public name:</strong>
+  <%= @donation.public_name %>
+</p>
+
+<%= link_to 'Edit', edit_admin_donation_path(@donation) %> |
+<%= link_to 'Back', admin_donations_path %>