[3.0] strict mode cleanup

[bajtos]

I am proposing to make a following change in 3.0:

• strict is not defined or is false - dynamic properties are supported (no change from 2.0)
• strict is true - dynamic properties are stripped and a validation error is reported (same as strict: 'validate' in 2.0)
• The other two modes from 2.0 (strict: true silently discarding values and strict: 'throw') should be removed.

@ritch @raymondfeng @fabien @clarkorz thoughts?

Tasks:

• make the change
• describe it in 3.0-RELEASE-NOTES.md
• update https://docs.strongloop.com/display/LB/Model+definition+JSON+file

[clark0x]

Does strict: true strip dynamic properties for schemaless datasource like mongodb?

Currently, strict does not affect for this kinds of data source.

[bajtos]

AFAIK, strict: true strips dynamic properties for all datasources, including mongodb. Note that the default value is connector-specific and defaults to false. SQL connectors set the value to true by default.

[davidcheung]

Info Placeholder
https://github.com/strongloop/loopback-datasource-juggler/blob/f102f6302b62640824584f50af3be52cdf7b27cd/lib/dao.js#L84-L104