Add special rendering for shop=computer

[kocio-pl]

We should start rendering shop=computer, probably with this icon from osmfr-cartocss fork:

https://github.com/cquest/osmfr-cartocss/blob/master/symbols/computer2.svg

[It was proposed in meta-issue #1402]

[kocio-pl]

Just a basically corrected version:

1. 
   or simpler one:
2. 
3. 

[matthijsmelissen]

I'm very busy at the moment, sorry for my lack of comments. I will get back to the PRs as soon as possible.

[kocio-pl]

Thanks for the message.

[daganzdaanda]

I'd take 2) or 3), even if that leaves a big "hole" in the icon.