feat(FastAPI): add /pkgbase/{name}/delete (get, post)

In addition, we've had to add cascade arguments to backref so
sqlalchemy treats the relationships as proper cascades.

Furthermore, our pkgbase actions template was not rendering
actions properly based on TU credentials.

Signed-off-by: Kevin Morris <kevr@0cost.org>

templates/packages/delete.html

@@ -0,0 +1,56 @@
+{% extends "partials/layout.html" %}
+
+{% block pageContent %}
+
+    {% if errors %}
+        <ul class="errorlist">
+            {% for error in errors %}
+                <li>{{ error | tr }}</li>
+            {% endfor %}
+        </ul>
+    {% endif %}
+
+    <div class="box">
+        <h2>{{ "Delete Package" | tr }}: {{ pkgbase.Name }}</h2>
+
+        <p>
+            {{
+                "Use this form to delete the package base %s%s%s and "
+                "the following packages from the AUR: "
+                | tr | format("<strong>", pkgbase.Name, "</strong>") | safe
+            }}
+        </p>
+
+        <ul>
+            {% for package in pkgbase.packages.all() %}
+                <li>{{ package.Name }}</li>
+            {% endfor %}
+        </ul>
+
+        <p>
+            {{
+                "Deletion of a package is permanent. "
+                "Select the checkbox to confirm action." | tr
+            }}
+        </p>
+
+        <form action="/pkgbase/{{ pkgbase.Name }}/delete" method="post">
+            <fieldset>
+                <p>
+                    <label class="confirmation">
+                        <input type="checkbox" name="confirm" value="1" />
+                        {{ "Confirm package deletion" | tr }}
+                    </label>
+                </p>
+
+                <p>
+                    <input class="button"
+                           type="submit"
+                           value="{{ 'Delete' | tr }}"
+                    />
+                </p>
+            </fieldset>
+        </form>
+
+    </div>
+{% endblock %}