Fixes #118

* Add customizable sbt keys for all template sources
* Make sure current template sources are used by default.
* Start on documentation for archetypes.
Updated documentation for overridable templates.

* Flesh out some more docs (barely) for archetypes
* Add a good bit of dcoumentation for how to override templates.
Fix location of templates to match documentation.
Bash configuration file now has a Key.

* Java App & Server archetypes can now configure default bash arguments
  via configuration file.
Merge pull request #121 from sbt/wip/overridable-script-templates

Allow script templates to be overridden