immutable -> read-only
Moved Gradle, Griffon, Maven and Ant to references and unlinekd from tutorials
Merge pull request #19 from JetBrains/referencing-tooling

Moved Gradle, Griffon, Maven and Ant to references and unlinked from tut...
Merge pull request #18 from JetBrains/read-only

immutable -> read-only
"Using properties" moved to appropriate place
Delegated properties