Refactor modules into contexts (#78)

* [WIP] break out a few contexts, start refactoring fast index modules

* [WIP] more contexts, this time around slow indexing and downloads

* [WIP] got all tests passing

* [WIP] Added moduledocs

* Built a genserver to rename old jobs on boot

* Added a module naming check; moved things around

* Fixed specs

lib/pinchflat/metadata/media_metadata.ex

@@ -0,0 +1,37 @@
+defmodule Pinchflat.Metadata.MediaMetadata do
+  @moduledoc """
+  The MediaMetadata schema.
+
+  Look. Don't @ me about Metadata vs. Metadatum. I'm very sensitive.
+  """
+
+  use Ecto.Schema
+  import Ecto.Changeset
+
+  alias Pinchflat.Media.MediaItem
+
+  @allowed_fields ~w(metadata_filepath thumbnail_filepath)a
+  @required_fields ~w(metadata_filepath thumbnail_filepath)a
+
+  schema "media_metadata" do
+    field :metadata_filepath, :string
+    field :thumbnail_filepath, :string
+
+    belongs_to :media_item, MediaItem
+
+    timestamps(type: :utc_datetime)
+  end
+
+  @doc false
+  def changeset(media_metadata, attrs) do
+    media_metadata
+    |> cast(attrs, @allowed_fields)
+    |> validate_required(@required_fields)
+    |> unique_constraint([:media_item_id])
+  end
+
+  @doc false
+  def filepath_attributes do
+    ~w(metadata_filepath thumbnail_filepath)a
+  end
+end