Assign Group Manager Pick Employee dropdown list improvements

[gjoverto]

Improve the Pick Employee dropdowns on the New Group Managers screen.

1. Order the list by name
2. Allow selecting a person who is already in the group
3. Enable type to functionality so employee names start appearing as the user is typing

[sibow]

The list is ordered by last name.
A person in the group can not manage a group because he/she can not approve his/her timesheet according to the roles