Formatting cards to be responsive

[iblancasa]

I am going to solve it

[abdonrd]

Thanks @iblancasa! But I just test the PR and there things that I don't like:

• The image-grid use Polymer 0.4. and the last commit is from 2014.
• The cards aren't centered. Image.
• There are errors in the Dev Tools. Image.

Sorry, but we need to find a best solution. 😕

[iblancasa]

Ok!