Add HWRP for configuring custom apps

Fixes #1 
Instead of this if construction, would it be understandable if we did something like this:

```ruby
file_name = @current_resource.local ? 'local' : 'default'
file_path = "#{@current_resource.apps_dir}/#{@current_resource.app}/metadata/#{file_name}.meta"
file = Chef::Resource::Template.new(file_path, run_context)
file.path(file_path)
```

(Could also inline the ternary operator in the `file_path` interpolation, but *eh*)