Hide t-shirt size selector when t-shirt's unwanted

Use Javascript to hide the t-shirt size selector when the the user
selects "No" for "Do you want a t-shirt?".  Reshow it (and make sure
it's shown by default) for "Yes".

www/conservancy/static/supporter-page.js

@@ -32,6 +32,16 @@ $(document).ready(function() {
         $control.find('.toggle-content').slideUp("slow");
         $control.find('.toggle-content').slideDown("slow");
     });
+    $(".t-shirt-size-selector").show();
+    $('input[name=os1]:radio').change(function() {
+        var input=$(this);
+        var value = input.val();
+        if (value == "Yes") {
+            $(".t-shirt-size-selector").show();
+        } else {
+            $(".t-shirt-size-selector").hide();
+        }
+    });
     $('#amount').addClass("valid");
     $('#amount').on('input', function() {
         var input=$(this);

www/conservancy/static/supporter/index.html

@@ -149,6 +149,7 @@ internal policies</a> are published and available for scrutiny.</p>
                       <input type="radio" checked="checked" name="os1" value="Yes" />Yes
                       <input type="radio" name="os1" value="No" />No
                       <br />
+                      <span class="t-shirt-size-selector">
                       <label for="wantGift"><strong>T-shirt size: </strong></label>
                       <input type="hidden" name="on3" value="size"/>
                       <select name="os3" id="os3">
@@ -161,7 +162,7 @@ internal policies</a> are published and available for scrutiny.</p>
                         <option name="os3" id="os3" value="LadiesM">Ladies' M</option>
                         <option name="os3" id="os3" value="LadiesL">Ladies' L</option>
                          <option name="os3" id="os3" value="LadiesXL">Ladies' XL</option>
-                      </select><br/>
+                      </select><br/></span>
                       <label for="publicAck"><strong>
                           Should we <a href="/sponsors#supporters">list you publicly</a> as a Conservancy Supporter? </strong></label>
                       <input type="hidden" name="on2" value="publicAck" />
@@ -202,6 +203,7 @@ internal policies</a> are published and available for scrutiny.</p>
                       <input type="radio" checked="checked" name="os1" value="Yes" />Yes
                       <input type="radio" name="os1" value="No" />No
                       <br />
+                      <span class="t-shirt-size-selector">
                       <label for="wantGift"><strong>T-shirt size: </strong></label>
                       <input type="hidden" name="on3" value="size"/>
                       <select name="os3" id="os3">
@@ -214,7 +216,7 @@ internal policies</a> are published and available for scrutiny.</p>
                         <option name="os3" id="os3" value="LadiesM">Ladies' M</option>
                         <option name="os3" id="os3" value="LadiesL">Ladies' L</option>
                          <option name="os3" id="os3" value="LadiesXL">Ladies' XL</option>
-                      </select><br/>
+                      </select><br/></span>
                       <label for="publicAck"><strong>
                           Should we  <a href="/sponsors#supporters">list you publicly</a> as a Conservancy Supporter? </strong></label>
                       <input type="hidden" name="on2" value="publicAck" />