Add two new snippets

[amercader]

• number.html for form fields that require a number value
• file_size.html to display resource sizes in a human friendly way

[wardi]

is there a validator that should go with the number input? Should the file size display snippet also be used in the example dataset schema?

[amercader]

@wardi We have the int_validator in core. I added the file size field to the example dataset schema

[wardi]

On second thought this adds a field to the form that we probably don't want (also I generally don't like the way number inputs are rendered with a little useless arrow controls). I think we're better without the ckan_dataset.yaml change.