Add option to enable the 'SMEI_SORT_DIRECTION' experiment

This option, when enabled, activates the SMEI_SORT_DIRECTION experiment,
which is disabled by default in the Community Console.

This experiment lets user set the sort direction in thread lists, so
threads can be ordered in ascending or descending order.

Fixes: #25
Change-Id: Ie8f6825e70d11ee7d3e20a38a7f20e2a34780d9f
diff --git a/src/options/options.html b/src/options/options.html
index 6edd040..15716da 100644
--- a/src/options/options.html
+++ b/src/options/options.html
@@ -32,6 +32,7 @@
       <div class="option"><input type="checkbox" id="ccforcehidedrawer"> <label for="ccforcehidedrawer" data-i18n="ccforcehidedrawer"></label></div>
       <div id="dragndrop-wrapper" class="option" hidden><input type="checkbox" id="ccdragndropfix"> <label for="ccdragndropfix" data-i18n="ccdragndropfix"></label></div>
       <div class="option"><input type="checkbox" id="batchlock"> <label for="batchlock" data-i18n="batchlock"></label> <span class="experimental-label" data-i18n="experimental_label"></span></div>
+      <div class="option"><input type="checkbox" id="smei_sortdirection"> <label for="smei_sortdirection" data-i18n="smei_sortdirection"></label> <span class="experimental-label" data-i18n="experimental_label"></span></div>
       <h4 data-i18n="profileindicator_header"></h4>
       <div class="option"><input type="checkbox" id="profileindicator"> <label for="profileindicator" data-i18n="profileindicator"></label> <span class="experimental-label" data-i18n="experimental_label"></span></div>
       <div class="option"><input type="checkbox" id="profileindicatoralt"> <label for="profileindicatoralt" data-i18n="profileindicatoralt"></label> <span class="experimental-label" data-i18n="experimental_label"></span></div>