Allow devs to use Java 6 with Gradle plugin.
Use tiered compilation for faster startup.

The JVM TieredCompilation flags switch the server VM to something that behaves
more like the client VM, including faster VM startup. Lazybones benefits more
from this than better optimised runtime performance.
Fix incremental build for integration tests.

I had failed to add the compiled app classes to the compilation classpath of
the integration tests, via the sourceset definition. This meant that modifying
application classes didn't trigger execution of the integration tests as Gradle
thought the integration test task was up to date.
Fix integration tests on Java 8.

Running the integration tests on the Java 8 VM resulted in lots of class
loading exceptions related to HashMap. This was because the integration tests
were running with version 2.0.5 of Groovy, which was pulled in by Spock. The
tests now run with the same version of Groovy as the app and other parts of the
build.
Tell user of potential Bintray metadata error.

Helps with issue #136, although there may be multiple reasons why the 'latest
version' might be null for a particular package.
Add runtime configuration manipulation.

Implements issue #118. This feature adds several commands to Lazybones:

    config set <option> <value1> ...
    config add <option> <value1> ...
    config clear <option>
    config show [--all] <option>
    config list

These commands allow users to access the saved Lazybones configuration without
diving into the standard user configuration file, ~/.lazybones/config.groovy.
In addition, it makes instructions for setting up additional template
repositories trivially easy:

    "Just run the command 'lazybones config add bintrayRepositories ...'"

The core of the implementation is a standalone `Configuration` class that does
most of the work of maintaining multiple configuration sources and ensuring
that users are aware when settings are overridden.

The class has an instance-level API that is agnostic of Lazbones, making it
reusable in other projects. The static properties and methods are definitely
Lazybones specific though.