Adjust date picker: Allow choosing years between 1027 and 2227

[christiansteinert]

The date picker when converting Western to Tibetan dates currently only allows convenient access to the date range 2003-2023.

If the year-dropdown in the date picker on the "Western Date -> Tibetan Date" tab should be adjusted to include years from 1027-2227 (inclusive) so that the entire date range that is supported by the application is conveniently available.