BHV-18764 : ExpandablePicker has backward capability issues regarding to...

... active property

## Issue
After https://github.com/enyojs/moonstone/pull/1740, enyo.Group.active is called before highlander property is set because bellowing binding is added in CheckboxItem
``` 
{from: 'active', to: '$.input.active', oneWay: false}
```
Thus, although multipleSelection is true, enyo.Group.active will handle it like multipleSelection: false

## Fix
Since this is timing issue, override initComponents() and mixing in the desired value for client.highlander

Enyo-DCO-1.1-Signed-off-by: SoonGil Choi (soongil.choi@lge.com)