takestamp should be a timestamp not a int

[ildyria]

Sswitching the format of photos.takestamp to timestamp instead of int() will allow us to search by date with the help of eloquent : https://laraveldaily.com/eloquent-date-filtering-wheredate-and-other-methods/

This also imply changing albums.min_takestamp and albums.max_takestamp to timestamp too.

[ildyria]

Done:
a4f9463
5d52c10

./artisan migrate will be (very) slow depending of the number of pictures on the server.
It needs to convert every single one of them one by one.

If someone has a more efficient solution for conversion, I will gladly take it.