Consistent website theme and custom 404 (apache#12426)

* consistent theme plus error handling for missing apis and pages

* add error pages

* update messaging

* force url update to 404 page on redirect

* static redirect to force url update

* version dropdown fix; reverts apache#12482; lesser of evils

* adding note to nudge past flakey test

docs/build_version_doc/AddVersion.py

@@ -74,8 +74,8 @@
                     version_tag_mobile.extract()
                 navbar.append(version_str)
                 navbar_mobile.append(version_str_mobile)
-                # The following causes rendering errors in code blocks; refer to #12168
-                #outstr = str(content).replace('&lt;', '<').replace('&gt;', '>')
+                # The following causes rendering errors in code blocks; refer to #12168 and #12524
+                outstr = str(content).replace('&lt;', '<').replace('&gt;', '>')
             # Fix link
             if args.current_version == tag_list[0]:
                 print("Fixing " + os.path.join(path, name))
@@ -114,4 +114,3 @@
 
             with open(os.path.join(path, name), "w") as outf:
                 outf.write(outstr)
-

docs/build_version_doc/artifacts/.htaccess

@@ -4,3 +4,10 @@ RewriteRule ^get_started.*$ /install/ [R=301,L]
 RewriteRule ^how_to.*$ /faq/ [R=301,L]
 RewriteRule ^api/python/symbol.html$ /api/python/symbol/symbol.html [R=301,L]
 RewriteRule ^community/index.html$ /community/contribute.html [R=301,L]
+RewriteRule ^versions/0.11.0/api/clojure/.*$ /error/api.html [R=301,L]
+RewriteRule ^versions/0.12.1/api/clojure/.*$ /error/api.html [R=301,L]
+RewriteRule ^versions/1.0.0/api/clojure/.*$ /error/api.html [R=301,L]
+RewriteRule ^versions/1.1.0/api/clojure/.*$ /error/api.html [R=301,L]
+RewriteRule ^versions/1.2.1/api/clojure/.*$ /error/api.html [R=301,L]
+
+ErrorDocument 404 https://mxnet.incubator.apache.org/error/404.html

docs/build_version_doc/build_all_version.sh

@@ -156,6 +156,7 @@ for key in ${!build_arr[@]}; do
     cp ../../settings.ini $tag/docs/
     cp ../../conf.py $tag/docs/
     cp ../../Doxyfile $tag/docs/
+    cp -a ../../_static $tag/docs/
 
     echo "Building $tag..."
     cd $tag/docs

docs/error/404.md

@@ -0,0 +1,3 @@
+# Page Does Not Exist
+
+If you're here that means you requested a page that doesn't exist. Sorry about that! Maybe try the search box to find what you're looking for, or navigate to the [Home Page](../index.html). Also, make sure you're looking in the correct version, as some features may only be available in [newer versions](https://github.com/apache/incubator-mxnet/releases) or the [master branch](../versions/master).

docs/error/api.md

@@ -0,0 +1,3 @@
+# API Not Available
+
+You selected an API that is not available for this version of MXNet. Try a more recent version of MXNet, or go to the [master](../versions/master/) version.