Machine card bugfixes

Solves the problem that the css output of a style card is not updated when you add a css card to a subordinate skin card of the style card.

The technical details:
The output file gets updated when a card was changed that is listed in the +input card of the machine card.
We save in the input cards only the cards that actually contribute to the output
(because for example we don't want the item list of a skin card in the css file). 
But this means when you add a new css card to a skin card the output of the style card won't be updated because the skin card is the only card that hears about the change and it won't pass the information on to the style card because it's not listed in the style's input card.

Solution:
Put all involved cards in the input card and use for the output only the items that are non-pointer cards.
The solution with card.left.refresh doesn't work. I'll put back the Wagn::Cache.reset_global until we find something better.

If a requested file doesn't exist, a file with the same name is created. The url points to a newer version.

This happened after I deleted all+*style+*machine_output-7152.css:
```
Started GET "/files/*all+*style+*machine_output-7154.css" for 127.0.0.1 at 2014-07-04 11:09:59 +0200
Processing by CardController#read as CSS
  Parameters: {"explicit_file"=>true, "id"=>"*all+*style+*machine_output", "rev"=>"7154"}
Sent file /Users/phi/dev/wagn/sites/coredev/files/1052/7154.css (0.3ms)
exception = ActionController::MissingFile: Cannot read file /Users/phi/dev/wagn/sites/coredev/files/1052/7154.css
[paperclip] Saving attachments.
[paperclip] Saving attachments.
[paperclip] saving /Users/phi/dev/wagn/sites/coredev/files/1052/7154.css
Redirected to http://localhost:3000/files/*all+*style+*machine_output-7156.css
```