Check packages for broken links when submitting for approval

Half of #546

app/templates/packages/view.html

@@ -221,7 +221,7 @@
 						</a>
 					{% endif %}
 					{% if package.forums %}
-						<a class="btn" href="https://forum.minetest.net/viewtopic.php?t={{ package.forums }}">
+						<a class="btn" href="{{ package.forums_url }}">
 							<i class="fas fa-comments"></i>
 							<span class="count">{{ _("Forums") }}</span>
 						</a>

app/templates/todo/topics_mismatch.html

@@ -54,7 +54,7 @@ Mismatched Topics
 					<div class="col-sm"></div>
 					<div class="col-sm-auto">
 						<a class="btn btn-secondary me-2" href="{{ package.get_url('packages.create_edit') }}">Edit</a>
-						<a class="btn btn-secondary me-2" href="https://forum.minetest.net/viewtopic.php?t={{ package.forums }}">Forums</a>
+						<a class="btn btn-secondary me-2" href="{{ package.forums_url }}">Forums</a>
 					</div>
 				</div>
 			</li>