add invite system

app/templates/users/sign_up.html

@@ -3,7 +3,13 @@
 {% block content %}
 <div class="darkbg login-container">
   <h1>Sign up</h1>
+  {% if inviter %}
+  <p>You have been invited by <a href="{{ url_for('users.page', username=inviter.username) }}">{{ inviter.username }}</a> to join {{ config.SITE_NAME }}. Create an identity below.</p>
+  {% endif %}
   <form method="post">
+    {% if key %}
+      <input type="hidden" value={{key}} name="key">
+    {% endif %}
     <label for="username">Username</label><br>
     <input type="text" id="username" name="username" pattern="[a-zA-Z0-9_-]{3,20}" title="3-20 characters. Only upper and lowercase letters, digits, hyphens, and underscores" required autocomplete="username"><br>
     <label for="password">Password</label>
@@ -12,6 +18,8 @@
     <input type="password" id="password-confirm" name="password-confirm" pattern="(?=.*[a-z])(?=.*[A-Z])(?=.*\d)(?=.*[\W_])(?!.*\s).{10,255}" title="10+ chars with: 1 uppercase, 1 lowercase, 1 number, 1 special char, and no spaces" required autocomplete="new-password"><br>
     <input type="submit" value="Sign up">
   </form>
+  {% if not inviter %}
   <span>After you sign up, a moderator will need to confirm your account before you will be allowed to post.</span>
+  {% endif %}
 </div>
 {% endblock %}