Manager/Admin adds User as Subordinate

[Zackeree]

MSS:

1. Manager/Admin views their Users(#35)
2. Manager/Admin selects User
3. Manager/Admin puts them as a subordinate (specifying under who if it’s an admin doing this)

Extensions:

3a: User is already a subordinate under someone else
    .1: Notify Manager/Admin
    .2: Manager/Admin may continue (some Users can have multiple managers/overseers) if they have permission

Requirements:

• [ ] Manager/Admin searches for User (#35)
• [x] UserControl addSubordinate method
• [x] Add Subordinate Insert
• [x] Subordinates table (user_id, user_id, with one as manager/overseer, other as subordinate)