Columns validations

Support column validations, code looks like:
```typescript
@Entity()
class E {
    @Column
    @Length(1, 10)
    name: string;

    @Column
    @IsDate()
    regDate: Date;
}
```
References to this project,
https://github.com/pleerock/class-validator

We should think about the way we implement it, should we just use the Sequelize embedded validator or using 3rd party one.