Support for Select All Filtered #46

Can we add the capability to select all filtered options?

Currently, it's possible to filter options using keywords, which updates SelectList accordingly. However, the SelectItem associated with the "select all" checkbox only operates on the original options, rather than the filtered options.

To accomplish this goal, we can make some changes to the allAreSelected(), selectAll, and selectNone methods in SelectPanel to make use of this.filteredOptions() instead of props.options.