add db models, refactor json models, add references in migrations

db/migrations/000003_create_systems.up.sql

@@ -1,12 +1,13 @@
 CREATE TABLE IF NOT EXISTS systems (
     id INTEGER PRIMARY KEY AUTOINCREMENT,
+    state_id INTEGER NOT NULL,
     text_id VARCHAR(256) NOT NULL,
     title VARCHAR(256) NOT NULL,
     description TEXT NOT NULL,
     url VARCHAR(256) NOT NULL, 
     download VARCHAR(256) NOT NULL,
-
-    created_at DATETIME NOT NULL DEFAULT current_timestamp
+    created_at DATETIME NOT NULL DEFAULT current_timestamp,
+    FOREIGN KEY (state_id) REFERENCES foundry_state(id) ON DELETE CASCADE
 );
 
 CREATE TABLE IF NOT EXISTS systems_compatibility (