Move admin proposals index view to a component

This way we can use the `header` method to simplify it a bit.

app/components/admin/proposals/index_component.html.erb

@@ -0,0 +1,39 @@
+<% provide :main_class, "admin-proposals-index" %>
+
+<%= header %>
+
+<% if proposals.any? %>
+  <%= render Admin::SearchComponent.new(label: t("admin.shared.search.label.proposals")) %>
+
+  <h3><%= page_entries_info proposals %></h3>
+
+  <table>
+    <thead>
+      <tr>
+        <th class="text-center"><%= t("admin.proposals.index.id") %></th>
+        <th><%= Proposal.human_attribute_name(:title) %></th>
+        <th><%= t("admin.proposals.index.author") %></th>
+        <th><%= t("admin.proposals.index.milestones") %></th>
+        <th><%= t("admin.proposals.index.selected") %></th>
+      </tr>
+    </thead>
+
+    <tbody>
+      <% proposals.each do |proposal| %>
+        <tr id="<%= dom_id(proposal) %>" class="proposal">
+          <td class="text-center"><%= proposal.id %></td>
+          <td><%= link_to proposal.title, admin_proposal_path(proposal) %></td>
+          <td><%= proposal.author.username %></td>
+          <td><%= proposal.milestones.count %></td>
+          <td><%= render Admin::Proposals::ToggleSelectionComponent.new(proposal) %></td>
+        </tr>
+      <% end %>
+    </tbody>
+  </table>
+
+  <%= paginate proposals %>
+<% else %>
+  <div class="callout primary">
+    <%= t("admin.proposals.index.no_proposals") %>
+  </div>
+<% end %>

app/components/admin/proposals/index_component.rb

@@ -0,0 +1,12 @@
+class Admin::Proposals::IndexComponent < ApplicationComponent
+  include Header
+  attr_reader :proposals
+
+  def initialize(proposals)
+    @proposals = proposals
+  end
+
+  def title
+    t("admin.proposals.index.title")
+  end
+end