Make headline images explicit, add asset credits

- related_assets gains a `headline` boolean (DB-enforced: at most one
  per page), replacing "first image by position" as the headline
  rule. A rake task backfills the current first image on every live
  head/draft, so nothing changes visually until an editor changes it.
- The image picker sidebar gets a star toggle reflecting the flag;
  the TinyMCE inline-image picker's badge now reads it too, instead
  of assuming position 0.
- No headline chosen (or none attached) now falls back to the
  gallery-count caption itself becoming the lightbox trigger, instead
  of the gallery being unreachable.
- Assets gain creator, source_url, and license_key (against a new
  config/asset_licenses.yml dictionary). asset_credit renders a
  degrading attribution line, reused as a hidden per-image glightbox
  caption so credit is one click away for every image, not only the
  headline's always-visible one.
- Fixed: asset thumbnails rendered unconditionally regardless of
  whether a real variant exists on disk. Asset#has_variant? checks
  file existence, not content type -- some legacy PDFs have real
  pre-rewrite thumbnails a content-type check would have hidden.
- assets#new/edit rebuilt onto the same node_description/node_content
  layout as assets#show, picking up the three new fields in the
  process.

1 files changed, 22 insertions, 1 deletions

diff --git a/test/models/asset_test.rb b/test/models/asset_test.rb
index a1041e45..d246abe0 100644
--- a/test/models/asset_test.rb
+++ b/test/models/asset_test.rb
@@ -19,5 +19,26 @@ class AssetTest < ActiveSupport::TestCase
     assert_equal 0, draft.assets.length
     assert_equal 0, RelatedAsset.count
   end
-  
+
+  test "image? is true for supported image content types" do
+    assert Asset.new(:upload_content_type => "image/png").image?
+    assert Asset.new(:upload_content_type => "image/jpeg").image?
+  end
+
+  test "image? is false for non-image content types" do
+    assert_not Asset.new(:upload_content_type => "application/pdf").image?
+    assert_not Asset.new(:upload_content_type => nil).image?
+  end
+
+  test "license_key must be a known dictionary key" do
+    asset = Asset.new(:license_key => "not_a_real_license")
+    I18n.with_locale(:en) do
+      assert_not asset.valid?
+      assert_includes asset.errors[:license_key], "is not included in the list"
+    end
+  end
+
+  test "license_key may be blank" do
+    assert Asset.new(:license_key => nil).valid?
+  end  
 end