boostrap: Reset to v2.3.2.

We merge bootstrap-responsive.css into bootsrap.css since that is
how bootstrap distributes it from this version onwards.

bootstrap.js has a lot of changes to it which completely breaks
our typeaheads and popovers, so we will have to override these
plugins with our version of these plugins. In future versions
of bootstrap when we use npm, we can just choose not to
import them.

docs/THIRDPARTY

@@ -77,7 +77,7 @@ Files: static/third/bootstrap/css/bootstrap-btn.css
 Copyright: 2011-2014 Twitter, Inc
 License: Expat
 
-Files: static/third/bootstrap/css/bootstrap-responsive.css static/third/bootstrap/css/bootstrap.css
+Files: static/third/bootstrap/css/bootstrap.css
 Copyright: 2012 Twitter, Inc
 License: Apache-2.0
 Comment: The software has been modified.

static/js/bundles/common.js

@@ -9,7 +9,6 @@ import "../../third/bootstrap/js/bootstrap.js";
 import "../common.js";
 import "../../third/bootstrap/css/bootstrap.css";
 import "../../third/bootstrap/css/bootstrap-btn.css";
-import "../../third/bootstrap/css/bootstrap-responsive.css";
 import "simplebar/dist/simplebar.css";
 import "font-awesome/css/font-awesome.css";
 import "../../assets/icons/zulip-icons.font.js";