Install refactoring

Can't we just call the recipes multiple times? Installation should be skipped automatically if a package is already installed (or we should manually check).
This is not reliable, as `node['recipes']` probably only checks for recipes enabled in the node configuration, if installation is called from e.g. a wrapper cookbook, `node['recipes']` will never know...

I think we can simply this to e.g.

```ruby
include_recipe 'duplicity_ng::install_ftp' if new_resource.backend.include?('ftp://')
```