Implement assignment import and clear of budget

postgres/schema/202112071547_assignments.sql

@@ -0,0 +1,11 @@
+-- +goose Up
+CREATE TABLE assignments (
+        id uuid DEFAULT uuid_generate_v4() PRIMARY KEY,
+        category_id uuid NOT NULL REFERENCES categories (id),
+        date date NOT NULL,
+        memo text,
+        amount decimal(12,2) NOT NULL
+);
+
+-- +goose Down
+DROP TABLE assignments;