Fix permission group select v-autocomplete behaviour

The v-autocomplete component used in the PermissionGroupSelect doesn't show the options anymore when the multiple flag is used. I've switched to v-select which hasn't the ability to filter the options but still works with multiple.

Example

Doesn't work

<v-autocomplete
  :items="[{text: 'foo', value: 1}]"
  label="Permission groups"
  multiple
/>

Works

<v-select
  :items="[{text: 'foo', value: 1}]"
  label="Permission groups"
  multiple
/>