Issue #207: the menu fixes never end

- Resurrect add subreddit item since it's convenient
- Hide new post icon when searching a subreddit
Issue #207: remove unused strings and icons

The queue icon wasn't good for the add subreddit action, and we never
added a "Help" function anyway.
Issue #205: remove ViewPager on single pane search

Posts are already swipable so being able to swipe between tabs makes it
more confusing and glitchy. It's also more consistent, because the large
screen search doesn't allow you to swipe between tabs.