Incorporate test templates into app build.

The app build now packages and installs the test templates itself, which means
that it no longer depends on the templates project.
Add support for multiple template engines.

Implements issue #52. It's now possible to register template engines against
specific suffixes. The `processTemplates()` method available to post-install
scripts will then use those template engines for matching files that have the
corresponding file suffix.

The old behaviour is still available via the default template engine, which is
of course still Groovy's `SimpleTemplateEngine`. You can change the default
though if, for example, you want to only use Handlebars templates.

This change has complicated the way that templates are processed, so you should
review the new behaviour in the [template developers guide](https://github.com/pledbrook/lazybones/wiki/Template-developers-guide).
Add Andy Duncan as contributor.