Indicate if "numTotalResults" is an approximated count in VariantQueryResult

[j-coll]

An approximated count was added in #638 as part of the integration with Solr. This will return an approximation count with about 1% of error, we need to inform users if the numTotalResults returned is exact or an approximation.

This approximateCount will be executed if the VariantStorageEngine intersects results from Solr and MongoDB and the param "approximateCount" is true.
It may happen that, even if the param "approxCount" is present, the result is not approximated (the number of samples was bigger than the totalCount, or the query went entirely to Solr. For this situations, it will be interesting to have a boolean field in VariantQueryResult indicating this.

• Add boolean field to specify if the total count (if any) is approximated or not
• Add sampling size for the approximate count

[imedina]

With this the Variant query result returned will look like this:

{
id: "",
dbTime: 13,
numResults: 10,
numTotalResults: 5643,
approximateCount: true,
warningMsg: "Data from Solr + mongodb",
errorMsg: "",
resultType: "org.opencb.biodata.models.variant.Variant",
result: [...]
}

where the 5643 of numTotalResults is an aproximation with ~1% error.