GORA-656 Add Hazelcast Imap backed datastore

[saviyo]

Google Summer of Code 2020 project - Hazelcast IMAP based cache datastore for Apache Gora.

[djkevincr]

@saviyo Thank you for your hard work during the GSoC period. PR looks very good. I m going to keep PR for a while for let others to review. There are certain cases which I find can further be improved, I will do a full review on next few days. Good Luck with your final evaluation.

[lewismc]

@saviyo the following problem seems to be failing build

Error:  Failed to execute goal on project gora-solr: Could not resolve dependencies for project org.apache.gora:gora-solr:bundle:1.0-SNAPSHOT: Failed to collect dependencies at org.apache.solr:solr-core:jar:8.0.0 -> org.restlet.jee:org.restlet:jar:2.3.1: Failed to read artifact descriptor for org.restlet.jee:org.restlet:jar:2.3.1: Could not transfer artifact org.restlet.jee:org.restlet:pom:2.3.1 from/to maven-default-http-blocker (http://0.0.0.0/): Blocked mirror for repositories: [maven-restlet (http://maven.restlet.org, default, releases+snapshots), apache.snapshots (http://repository.apache.org/snapshots, default, disabled)] -> [Help 1]

Any ideas what is going on?