Change models, new migrations, fix front and make tests work

Signed-off-by: Thomas Citharel <tcit@tcit.fr>

priv/repo/migrations/20180110095317_create_members.exs

@@ -0,0 +1,17 @@
+defmodule Eventos.Repo.Migrations.CreateMembers do
+  use Ecto.Migration
+
+  def change do
+    create table(:members, primary_key: false) do
+      add :role, :integer
+      add :group_id, references(:groups, on_delete: :nothing)
+      add :account_id, references(:accounts, on_delete: :nothing)
+
+      timestamps()
+    end
+
+    create index(:members, [:group_id])
+    create index(:members, [:account_id])
+
+  end
+end