Remove the embed.rb in favor of `ln`-solution

[tordans]

I am pretty sure the embed plugin is the reason why the collection-objects are more ore less broken.
The issue is, that for site.haushalte one url/page is included 3 times. My understanding is, that collections should not behave like this. To work around this issue, there are many places in the code that check for layout = 'budget2' or something similar which is a huge code small but also makes it really time consuming to develop in this Jekyll.
Lastly, it breaks external plugins.

Possible solutions

• Maybe use the ln-solution from jekyll/jekyll#3041 (comment)
• Maybe build a custom deploy script that copies the content of /haushalte/ to the two other folders and only then calls jekyll build.