Add Currency entity to database

db/currency.go

@@ -0,0 +1,14 @@
+package db
+
+import "gorm.io/gorm"
+
+type Currency struct {
+	gorm.Model
+	Name    string
+	ISOName string
+	Symbol  string
+}
+
+func (c Currency) GetID() uint {
+	return c.ID
+}

db/db.go

@@ -70,6 +70,7 @@ func Connect() *gorm.DB {
 	gormDB.AutoMigrate(&Session{})
 	gormDB.AutoMigrate(&Expense{})
 	gormDB.AutoMigrate(&Metric{})
+	gormDB.AutoMigrate(&Currency{})
 	return newUDB
 }