Fix Redirects and Move PyTorch Versions to Getting Started (#83)

While working on moving PyTorch versions to a tab in Getting Started, and setting up a redirect from the old page, I noticed that the docs redirect (with `redirect_url` was clashing with the default redirects using `redirect_from` - if you look at the prod site, you will notice that the latter redirects do not work any longer). So, I changed the layout name of the redirect for docs to `docs_redirect.html` and then the others use the default redirect mechanism provided by the redirect plugin.

Author: JoelMarcey

_get_started/get-started-via-cloud-partners.md

@@ -1,6 +1,6 @@
 <p>Select your preferences and run the install command. Please ensure that you are on the latest pip and numpy
   packages. Anaconda is our recommended package manager. You can also
-  <a href="{{ site.baseurl }}/previous-versions">install previous versions of PyTorch.</a>
+  <a href="{{ site.baseurl }}/get-started/previous-versions">install previous versions of PyTorch.</a>
 </p>
 
 <div class="row">

_get_started/get-started-via-colab.md

@@ -8,7 +8,7 @@ <h3>Quick Start
 
         {% include quick_start_local.html %}
 
-        <br/><a href="{{ site.baseurl }}/previous-versions">Previous versions of PyTorch</a>
+        <br/><a href="{{ site.baseurl }}/get-started/previous-versions">Previous versions of PyTorch</a>
       </div>
 
       <div class="col-md-4 offset-md-2 cloud-options-col">