"Entity of type tag with id/null was not found" Error When Trying To Add Deleted Tag

[LeoNerdoG]

If user tries to add a tag to a device, that has been deleted (e.g. from another browser), Kapua returns an error that this Tag cannot be found.
I suggest we modify this somehow so at least the field is coloured in red (error state) or even better - that window closes and Kapua returns a smiliar error to existing one.

Testflow:

1. Login as kapua-sys or any other user that has proper permissions
2. Go to Tags, add a tag (e.g. tag0)
3. Go to Device create a device (e.g. device0) and go to its Tags tab click Add and select tag0
4. Now open kapua in new browser (e.g. Chrome or Opera), login as kapua-sys and go to Tags.
5. Select tag0 and delete it.
6. Now go back to the first browser and try to add the deleted tag.

Expected behavior
Kapua should close the Add tag window and report that "tag is not available/missing" or something similar.

Screenshots

Version of Kapua
1.1.0-SNAPSHOT

Type of deployment
[ ] Local Vagrant deployment
[x] Docker
[ ] Openshift (in its variants)
[ ] Others

Main component affected
[x] Console (in case of console please report info on which browser you encountered the problem)
[ ] REST API
[ ] Message Broker
[ ] - Others

Browsers used:

• Google Chrome (Version 69.0.3497.100 (Official Build) (64-bit))
• Safari (Version 12.0 (13604.3.5))
• Mozilla Firefox (63.0 (64-bit))
• Opera (Version 55.0.2994.44)

[LeoNerdoG]

I have verified that this issue has been resolved.