Scoped model members #35

As discussed earlier today, it would be nice to have model members that are scoped for overlying components. Example:

cs(this).model({
  'state:data-loaded@entityList'     : { value: false, valid: 'boolean' },
  'state:data-loaded@detailsView'  : { value: false, valid: 'boolean' }
})

Both model members have the same label but are only visible for the sub-tree, specified after the @ symbol.