[codegen] InlineModelResolver doesn't copy `required` parameter to new reference property

Description

https://github.com/swagger-api/swagger-codegen/blob/v2.2.1/modules/swagger-codegen/src/main/java/io/swagger/codegen/InlineModelResolver.java#L249 Here new reference property is created instead on inline object property. But flag required is not copied to newly created property definition. It leads that generated model is not relevant to swagger description.

Also in ModelImpl - https://github.com/swagger-api/swagger-core/blob/v1.5.10/modules/swagger-models/src/main/java/io/swagger/models/ModelImpl.java#L176 the list of required fields is calculated according to properties, not appropriate variable - https://github.com/swagger-api/swagger-core/blob/v1.5.10/modules/swagger-models/src/main/java/io/swagger/models/ModelImpl.java#L22 It looks like data duplication (list and value in properties), I would remove the list.

Swagger-codegen version

2.2.1 and current master