Allow "now" option for date range

Problem/Motivation

The date range widget has an option to control the range of year values allowed, with a default of 1900 to 2050. However, it isn't possible to set it to not allow future dates, for scenarios where you need to have a maximum of the current year.

Proposed resolution

Provide an option to have the end year be the current year, e.g. "now".

Remaining tasks

Work out how to do this.

User interface changes

The date range would allow filling in "now" to indicate the current year.

API changes

TBD

Data model changes

TBD