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

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

priv/repo/migrations/20180112105354_create_sessions.exs

@@ -0,0 +1,24 @@
+defmodule Eventos.Repo.Migrations.CreateSessions do
+  use Ecto.Migration
+
+  def change do
+    create table(:sessions) do
+      add :title, :string
+      add :subtitle, :string
+      add :short_abstract, :text
+      add :long_abstract, :text
+      add :language, :string
+      add :slides_url, :string
+      add :videos_urls, :string
+      add :audios_urls, :string
+      add :begins_on, :datetimetz
+      add :ends_on, :datetimetz
+      add :event_id, references(:events, on_delete: :delete_all), null: false
+      add :track_id, references(:tracks, on_delete: :delete_all)
+      add :speaker_id, references(:accounts, on_delete: :delete_all)
+
+      timestamps()
+    end
+
+  end
+end