Introduce ability to detect installed Java versions for a Platform

[brianoliver]

As a developer, often I'd like to launch Java applications using a specific version of Java. Currently to achieve this I need to specify the JAVA_HOME, but ultimately I'd prefer it if Bedrock could auto-detect (through some mechanism) the installations of Java available and then allow my applications to simply state the version(s) that could be used.

eg: platform.launch(JavaApplication.class, JavaVersion.of("1.8"));

One possible approach is to allow the definition of these using some property file, like the Maven Tool Chain, eg: a ~/.bedrock-settings.xml, or alternatively, attempt to use the Maven Tool Chain (when detected / available or using Maven profiles). Alternatively Bedrock could look in "standard" places for the platform and infer the installations. This is easy for most platforms, especially OS/X.