Tools: Update to new dockerhub everywhere

[apeltzer]

Since we switched, we should replace docker hub with docker cloud everywhere in the docs etc.
Would be quite a nice test case for the new automation :-)

[ewels]

Now that the _new_ dockerhub is released and docker cloud is being discontinued (🤦‍♂️) we should switch to dockerhub everywhere I guess.

[apeltzer]

Could we introduce a variable somewhere and then make future switching super-easy? :-D

[ewels]

Hopefully there will not be any future switching!

[apeltzer]

This is done everywhere, also in the TEMPLATE