This PR improves object's types.

Before

1. regular object - output schema is any

const testSchema = Joi.object({ FOO: 'bar' });

2. with keys - output schema is any
   

3. with append - output schema not changed
   

4. with rename - no key completion, output schema not changed
   

5. with with - no key's completion
   

6. with without - no key's completion
   

After

1. regular object usage incorporates the object type that was passed
   
   which means that calling to attempt returns the object type properly
   

2. using keys
   without provided object
   
   extending provided object
   

3. with append
append with null or undefined not changing the original obj
   
   appending new object keys
   

4. with rename - key completion, output schema changed
   
   

5. with with - key completion
   
   completes the rest of the keys (since .with('foo', 'foo') doesn't make sense)
   

6. with without - same as with
   
   

closes #2978