Fix timeouts in source:<url> searches and bookmarklet.

* Change the source index on posts from `(lower(source) gin_trgm_ops) WHERE source != ''`
  to just `(source gin_trgm_ops)`. The WHERE clause prevented the index
  from being used in source:<url> searches because we didn't specify
  the `source != ''` clause in the search itself. Excluding blank
  sources only saved a marginal amount of space anyway. This fixes
  timeouts in source:<url> searches and in the bookmarklet (since we do
  a source dupe check on the upload page too).

* Also switch from indexing `lower(name)` to `name` on pools and users.
  We don't need to lowercase the column because GIN indexes can be used
  with both LIKE and ILIKE queries.

app/models/pool.rb

@@ -47,7 +47,7 @@ class Pool < ApplicationRecord
     def name_matches(name)
       name = normalize_name_for_search(name)
       name = "*#{name}*" unless name =~ /\*/
-      where("lower(pools.name) like ? escape E'\\\\'", name.to_escaped_for_sql_like)
+      where_ilike(:name, name)
     end
 
     def default_order
@@ -108,7 +108,7 @@ class Pool < ApplicationRecord
     if name =~ /^\d+$/
       where("pools.id = ?", name.to_i).first
     elsif name
-      where("lower(pools.name) = ?", normalize_name_for_search(name)).first
+      where_ilike(:name, normalize_name_for_search(name)).first
     else
       nil
     end