disable google+ signup and listen UI

...in preparation for google shutting it down entirely. #846

templates/about.html

@@ -51,6 +51,7 @@
 <li><a href="#history">How long has this been around?</a></li>
 <li><a href="#stats">How big is this?</a></li>
 <li><a href="#rip-facebook">What happened to Facebook?</li>
+<li><a href="#rip-google+">What happened to Google+?</li>
 <li><a href="#profile-link">Why does my web site URL need to be in my social
   network profile?</a></li>
 <li><a href="#add-remove-url">How do I add or remove a web site URL from
@@ -252,6 +253,14 @@
 </p>
 </li>
 
+<li id="rip-google+" class="question">What happened to Google+?</li>
+<li class="answer">
+<p>Google+, at least the "consumer" version, will soon cease to exist. So long, and thanks for all the fish!</p>
+
+<p>Bridgy included support Google+ from the very beginning, <a href="https://snarfed.org/2012-01-08_bridgy_launched">when it launched in January 2012</a>. Sadly, Google <a href="https://blog.google/technology/safety-security/expediting-changes-google-plus/">plans to shut down consumer Google+ in April 2019</a> and <a href="https://developers.googleblog.com/2018/12/google-apis-shutting-down-march-7-2019.html">turn off the API earlier, in February</a>. Gory details in <a href="https://github.com/snarfed/bridgy/issues/846">this issue</a>. RIP, we'll miss you!
+</p>
+</li>
+
 <li id="profile-link" class="question">Why does my web site URL need to be in my
   social network profile?</li>
 <li class="answer">

templates/googleplus_signup.html

@@ -1,8 +1 @@
-<!-- Google+ listen signup -->
-<form method="post" name="listen-googleplus-start" action="/googleplus/start" class="signup">
-  <input type="image" alt="Sign in with Google+"
-         src="/oauth_dropins/static/google_plus.png" />
-  <!-- The state param doesn't actually work for G+. Not sure why. Doesn't
-       matter for now since we don't support publish for G+. -->
-  <input name="feature" type="hidden" value="listen" />
-</form>
+<a title="Google+ is dead 😢" href="/about#rip-google+"><img class="shadow" src="/static/google_plus_bw.png" /></a>

templates/social_user.html

@@ -11,6 +11,14 @@
 </div>
 {% endif %}
 
+{% if source.SHORT_NAME == 'googleplus' %}
+<div class="row promo error">
+<p><b><a href="/about#rip-google+">Google+ won't exist for much longer.</a>
+So long, and thanks for all the fish!</b></p>
+</div>
+{% endif %}
+
+
 {% if "listen" in source.features %}
 {% if source.is_private() %}
 <div class="row promo warning">
@@ -71,7 +79,7 @@
 
 <div class="row">
 
-{% if source.SHORT_NAME != 'facebook' %}
+{% if source.SHORT_NAME not in ('facebook', 'googleplus') %}
 <!-- Listen UI -->
 <div id="listen-ui" class="{% if publish_signup_ok %}col-sm-6{% endif %}">
 
@@ -257,7 +265,7 @@
 </div>
 
 </div>
-{% endif %}
+{% endif %} {# end Facebook/Google+ hiding UI blocks #}
 
 
 <!-- Publish preview UI -->