Yanked crates shouldn't be displayed on user/team pages

[carols10cents]

Related to #145.

Since we currently only keep track of yanked-ness on version records rather than on crate records, implementing this involves:

• Changing the query for the crates a user owns and the query for the crates a team owns to have an additional condition that there must be at least one version associated with that crate that has yanked equal to false.
  • I expect figuring out the diesel incantation to express this condition to be the most difficult part of this issue; give it a try and post what you've tried and I can help figure it out if you get stuck!
• Make a new test similar to this one that if the user or team in the test owns a crate where all versions have been yanked, that crate does NOT show up in the JSON response.

[sodiumjoe]

I'd like to give this a shot.

[sgrif]

Is there ever a case where we want the /crates route to include yanked crates? If not something like this should do it:

diff --git a/src/krate/search.rs b/src/krate/search.rs
index 3a8030a..dfa59d0 100644
--- a/src/krate/search.rs
+++ b/src/krate/search.rs
@@ -50,6 +50,11 @@ pub fn search(req: &mut Request) -> CargoResult<Response> {
     let recent_downloads = sql::<Nullable<BigInt>>("SUM(crate_downloads.downloads)");
 
     let mut query = crates::table
+        .filter(exists(
+            versions::table
+                .filter(versions::crate_id.eq(crates::id))
+                .filter(versions::yanked.eq(false)),
+        ))
         .left_join(
             crate_downloads::table.on(
                 crates::id