Merge pull request #115 from camilotorresf/fixes

Fixes
In database, add the date and time when the user first registered
Remove duplicate tags in category listing
Loading image in category listing

Have a loading screen while the category is loading so it's not a blank space.
Load 30 items at a time in category listing

And fix automatic loading of images on scroll to bottom
Show the items in each column more balanced

Show the items more well distributed along the columns
Fix admin pin edit for pins without price
Show a loading at the bottom of the category listing

This is an image to show when loading more items.