Revert deprecation of the 'list' option

The list option was accidentally deprecated, because I thought infinite
scrolling was implemented both in the Community Console and TW. However,
that was only implemented in the CC and not in TW, where the feature is
still being added by this extension.

This commit, therefore, readds the list option, which should be enabled
by default, except if the user disabled it before the option was
deprecated by accident.

Change-Id: Ibdaa109ca071105b060c63e848867381618288a1
diff --git a/src/options.html b/src/options.html
index 3df88c5..021db05 100644
--- a/src/options.html
+++ b/src/options.html
@@ -7,6 +7,7 @@
+      <input type="checkbox" id="list"> <label for="list" data-i18n="list"></label><br>
       <input type="checkbox" id="thread"> <label for="thread" data-i18n="thread"></label><br>
       <input type="checkbox" id="threadall"> <label for="threadall" data-i18n="threadall"></label>