Fixes sections on core concepts section
Adds gradle support - checkstyle, jacoco code coverage, maven publishig.

Adds checkstyle code quality checks

Adds jacoco test coverage plugin

Adds publishing (artifactory)

Fails build on jacoco coverage failures

Ignoring more idea files
Adds maven provided scope to pom dependencies
Externalizes maven pom filtering and sets groovy-all dependency to test.
Publishing to https://oss.jfrog.org (not yet bintray)
Publishes release artifacts to bintray