Fix User search.

Now uses a trigram based search. This is a lot faster and gives better
results. Closes #185.

priv/repo/migrations/20180516144508_add_trigram_extension.exs

@@ -0,0 +1,15 @@
+defmodule Pleroma.Repo.Migrations.AddTrigramExtension do
+  use Ecto.Migration
+  require Logger
+
+  def up do
+    Logger.warn("ATTENTION ATTENTION ATTENTION\n")
+    Logger.warn("This will try to create the pg_trgm extension on your database. If your database user does NOT have the necessary rights, you will have to do it manually and re-run the migrations.\nYou can probably do this by running the following:\n")
+    Logger.warn("sudo -u postgres psql pleroma_dev -c \"create extension if not exists pg_trgm\"\n")
+    execute("create extension if not exists pg_trgm")
+  end
+
+  def down do
+    execute("drop extension if exists pg_trgm")
+  end
+end

priv/repo/migrations/20180516154905_create_user_trigram_index.exs

@@ -0,0 +1,7 @@
+defmodule Pleroma.Repo.Migrations.CreateUserTrigramIndex do
+  use Ecto.Migration
+
+  def change do
+    create index(:users, ["(nickname || name) gist_trgm_ops"], name: :users_trigram_index, using: :gist)
+  end
+end