Make year range validation less strict by default.

Currently 1899 fails - which could be a valid date in some use cases.

Refs conversation around https://github.com/cakephp/cakephp/commit/33fbace4c77040acf2379bc1e9463e6f580feeef#commitcomment-7145913

Not sure if we should do that, though. But here is a better location for a discussion.

Anyway, since `2999` is the upper limit, it sounds silly to set the lower limit already at `1900`.
Especially as there is no use case for any such far away future dates, whereas years the distant past are quite important for a lot of use cases.
It should rather be `1000` then as lowest (4 digit) year possible.
But I did set it to `1800` now for 2.5, we can rediscuss it for 2.6 of course.