Template and task revamp

There was confusion around finding templates and tasks in cases of task inheritance. For one reason, tasks are referenced in their .yaml files by name, but are uniquely identified via name and os_version. Additionally, having the .yaml files separate from their respective template directory is counterintuitive. Now, yaml files have a consistent name (metadata.yaml) and exist alongside their templates in one self-containing task folder.

Included in this changeset is:
- Removing os_version from path
- Adding ".task" to task folder name
- Using "metadata.yaml" as a taskname convention inside task folder
- Allowing "/" and preventing "$" in task names.

Fixes https://tickets.puppetlabs.com/browse/RAZOR-154