Source attributes in output template (#45)

* Updated download options to take a media item; allowed for specifying custom output path template options

* Fixed bug where indexing job wouldn't run for the first time

* Renamed friendly_name to custom_name

* Added new options to default template and UI

* Improved explainer UI

test/support/fixtures/sources_fixtures.ex

@@ -19,7 +19,7 @@ defmodule Pinchflat.SourcesFixtures do
           collection_name: "Source ##{:rand.uniform(1_000_000)}",
           collection_id: Base.encode16(:crypto.hash(:md5, "#{:rand.uniform(1_000_000)}")),
           collection_type: "channel",
-          friendly_name: "Cool and good internal name!",
+          custom_name: "Cool and good internal name!",
           original_url: "https://www.youtube.com/channel/#{Faker.String.base64(12)}",
           media_profile_id: ProfilesFixtures.media_profile_fixture().id,
           index_frequency_minutes: 60