Create a widget for editing an amount and its unit of measurement. This can be

used for setting an integer amount that can be described in a set of units,

for example a number of days, weeks, months, years, or a number of bytes,

kilobytes, megabytes, etc. The widget has a number input and a dropdown select

which contains the units to choose from.

Ran unit tests.
Tested with the upcoming client web-based logon change for Review Board

  that uses the widget.