Implement rowlimit support in the yandex2 geocoder.

This commit adds rowlimit support to the yandex2 geocoder.

The code for rowlimit support is directly taken from the openlayers geocoder.

Actually, I don't like that code (it has «row_limit», «rowlimit», some geocoders use «this.row_limit» in the same place where other ones use just «rowlimit» and so on). Btw, «this.row_limit» logic is broken if multiple requests are done at the same time. I don't even see the purpose behind «me.row_limit» at all.

But I kept this this way because other geocoders share the same code.

Cleaning up geocoders is another issue, which I would prefer not to touch with this commit, and just stick with how things are now.