Add support for Solr 6.x/7.x

The initial PR on Solr was based on Solr 6.x, however at that time we supported Java 7 so Insisted to move it to Solr 5.x (which is Java 7 compatible). This issue is to add support for multiple versions of Solr ideally in a single module.

Notice that I was able to recover the original code for Solr 6.x created by [~caomanhdat] here (there are some differences in the way the Split was calculated and maybe some other minor things):(
[https://github.com/iemejia/beam/blob/recover-solrio/sdks/java/io/solr/pom.xml](https://github.com/iemejia/beam/blob/recover-solrio/sdks/java/io/solr/pom.xml)

This issue does not cover support for Solr 7, but if it is possible to add it as part of it, it would be great.

Imported from Jira [BEAM-3947](https://issues.apache.org/jira/browse/BEAM-3947). Original Jira may contain additional context.
Reported by: iemejia.