[#418] Change UserProfile field to match form

[just1602]

With those changes, the UserProfile model is matching the widgets.

• public_email is now an EmailField
• website is now an URLField
• website_rss is now an URLField

I let the max value of the year of birth to 2500 in the model, but I change it to be the current year minus 10 years, since Archlinux probably won't have any dev which are less than 10 years old, and it'd avoid garbage or error. There's probably a better way to enforce this more strictly than in the HTML, but I guess it's better than nothing.

I have only kept the migrations related to the changes I made. I'll open other PRs for the year of birth migration change and another one that was pending.