Add object type guards schema

[petrenkoVitaliy]

Fixes part of #2622 with adding objectSchema's type check.

Type validation will check all properties on existence and correct schema.
Extra parameters don't cause errors and there are may be smth missing in the ObjectPropertiesSchema

Usage:

interface ObjType {
  firstName: string;
  lastName: string;
  nestedObject: {
    middleName: string;
  }
}

// no errors
Joi.object<ObjType, true>({
  firstName: Joi.string(),
  lastName: Joi.string(),
  nestedObject: Joi.object<ObjType['nestedObject'], true>({
    middleName: Joi.string()
  })
})

// error -> 'lastName' is missing
Joi.object<ObjType, true>({
  firstName: Joi.string(),
  nestedObject: Joi.object<ObjType['nestedObject'], true>({
    middleName: Joi.string()
  })
})

// error -> 'lastName' has incorrect shema type
Joi.object<ObjType, true>({
  firstName: Joi.string(),
  lastName: Joi.number(),
  nestedObject: Joi.object<ObjType['nestedObject'], true>({
    middleName: Joi.string()
  })
})

[hueniverse]

Can I get a 👍 from someone who knows TS well?