Handle basic data incosistencies in restore

[juarezr]

Usually data inconsistencies happen when:

1. User changed core managed schema after imported documents
2. Target core has a schema with a subset of fields of source core schema

Data inconsistencies to handle:

1. Missing required fields in documents
2. Wrong value type for a field like string/int/float, string/datetime, etc...

Todo:

1. Detect data inconsistency while posting the Json batch of documents into the core update handler
2. Write inconsistent documents from the batch to a separated file
3. Check if remaining documents in the json batch are correctly stored into the core
4. Try to skip as many cases as possible

[juarezr]

Probably can work with a mecanism like transformations of #4 for filling/editing missing values.