Feature/finer template control

Everything under “Templates” in our API documentation is now implemented:
- List templates
- Get specific template
- Get specific template+version
- Update template version
- Create new template
- Create new template version
Even better, this could just be:

```
$endpoint="templates/" . $template_id

if($version_id) {
   $endpoint .= "/versions/" . $version_id;
}
```

Or something.