UI: System Allows Selection of Duplicate Enitity ID

Tested in version 1.0.1-SNAPSHOT-cf7f219 
 
Description
When selecting an Entity ID, the system allows the user to add a duplicate of a previously selected id. The Save button is disabled, but the user is not given an indication of why this is so.
 
Steps (Prerequisite: Metadata Provider has been ceated)

1. Log into UI
2. From Dashboard select the Metadata Providers tab
3. Click 'Manage Filters' button
4. Click 'Add Filter' button
5. Enter Filter Name
6. Enter 'zoom' in Entity ID search field and select 'https://ship.zoom.us'
7. Click Add Entity ID button
8. Repeat: enter 'zoom' and select 'https://ship.zoom.us' and click Add Entity ID button
    
   What is occurring:
   The system allows the user to add the duplicate Entity ID. Note that the 'Save' button is enabled after the first entity id addition, but is disabled when the duplicate is added.
    
   What is expected
   I see two possible ways to resolve the issue. The first seems best.
   1. Remove the item that has been already added from future search results.
   OR
   2. If a user chooses a duplicate, provide an error to indicate why Save button is disabled.
    
   Screenshot  
   Entity ID can be duplicated
    
   Video Attached
   Duplicate Entity ID Needs Error