feat(library): add games by name from IGDB

Games the user owns outside Steam get the key minus their
IGDB id, or the Steam appid when IGDB knows the game on
Steam. The sync never removes a MANUAL row and takes it
over once the user owns the game on Steam. Users without
a Steam ID can use the library.

src/main/resources/db/migration/V8__Manual_Games.sql

@@ -0,0 +1,8 @@
+-- Games the user adds by hand from IGDB, next to the Steam sync. The key stays appid: the Steam appid when IGDB
+-- knows the game on Steam, else minus the IGDB game id. So steam_game now also holds games that are not on Steam.
+ALTER TABLE user_game
+    ADD COLUMN source   VARCHAR(8)  NOT NULL DEFAULT 'STEAM',
+    ADD COLUMN platform VARCHAR(32);
+
+-- Picture for a game Steam has no art for, e.g. an IGDB artwork.
+ALTER TABLE steam_game ADD COLUMN image_url VARCHAR(512);