Make selectedOptionText parameter optional in adjustSelectWidth

Providing the parameter avoids multiple DOM accesses, but calling
the function is now more straightforward when the selected text
is unknown.
Extract adjustSelectWidth() from filter-utils to select-utils

I plan to reuse the function in group-by-category.
Add named function for onchange event handler of group selection
Adjust width of group selection list as selected value changes
Make selectedOptionText parameter required in adjustSelectWidth

I prefer to avoid extra DOM access as much as possible.

This reverts commit 714dbd2
Use non-breaking space by default in padding
Use NBSP constant defined in string-utils
Add a non-breaking space for padding at end of option to measure

The padding applied to the select appears after the arrow.
This extra character introduces padding between the selected
option and the arrow.

The result is more consistent in Firefox / Safari than defining
some padding-right on the option element.
Update display of the selected grouping criteria, next to the list

I considered extracting a function for this common processing
from filter-utils to select-utils, but the call only was more
complex than the inline code.
On reset, expand former option before selecting default value

Otherwise, the selected value would appear in the reduced form
in the list of options...