Have ESC zoom out topics if you're zoomed in.

This is the natural behavior that most users will
probably expect.  If you need to go to All Messages when
topics are zoomed in, you can just hit ESC twice.

static/js/hotkey.js

@@ -278,6 +278,11 @@ exports.process_escape_key = function (e) {
         return true;
     }
 
+    if (topic_zoom.is_zoomed_in()) {
+        topic_zoom.zoom_out();
+        return true;
+    }
+
     narrow.deactivate();
     return true;
 };

static/js/topic_zoom.js

@@ -4,6 +4,10 @@ var exports = {};
 
 var zoomed_in = false;
 
+exports.is_zoomed_in = function () {
+    return zoomed_in;
+};
+
 function zoom_in() {
     var stream_id = topic_list.active_stream_id();
 
@@ -16,7 +20,7 @@ function zoom_in() {
     zoomed_in = true;
 }
 
-function zoom_out() {
+exports.zoom_out = function () {
     var stream_li = topic_list.get_stream_li();
 
     popovers.hide_all();
@@ -28,7 +32,7 @@ function zoom_out() {
     }
 
     zoomed_in = false;
-}
+};
 
 exports.clear_topics = function () {
     var stream_li = topic_list.get_stream_li();
@@ -55,7 +59,7 @@ exports.initialize = function () {
     });
 
     $('.show-all-streams').on('click', function (e) {
-        zoom_out();
+        exports.zoom_out();
 
         e.preventDefault();
         e.stopPropagation();