Format numbers on admin donations page

And fix the wrong unit display in the user donations list.

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

@@ -5,7 +5,7 @@
     <thead>
       <tr>
         <th>User</th>
-        <th>Amount BTC (sats)</th>
+        <th>Amount BTC</th>
         <th>in EUR</th>
         <th>in USD</th>
         <th>Public name</th>
@@ -18,9 +18,9 @@
       <% @donations.each do |donation| %>
         <tr>
           <td><%= donation.user.cn %></td>
-          <td><%= donation.amount_sats %></td>
-          <td><%= donation.amount_eur %></td>
-          <td><%= donation.amount_usd %></td>
+          <td><%= sats_to_btc donation.amount_sats %> BTC</td>
+          <td><%= number_to_currency donation.amount_eur / 100, unit: "" %></td>
+          <td><%= number_to_currency donation.amount_usd / 100, unit: "" %></td>
           <td><%= donation.public_name %></td>
           <td><%= donation.paid_at ? donation.paid_at.strftime("%Y-%m-%d") : "" %></td>
           <td><%= link_to 'Show', admin_donation_path(donation) %></td>