Second part of harmonizing L2NM and L3NM according to the latest changes. Small fixes around the code.

Common:
- added slice to EventTools

OFC'22 tests:
- corrected OFC'22 delete service test to identify appropriate service to be deleted
- removed usage of events for testing

Compute:
- remove diversity constraint when not populated

Device:
- removed unused field in database and code polishing

Service:
- migrated L3NMEmulatedServiceHandler to the new API
- polishing of code

- Improved look & feel of service and slice pages.

Device:
- fixed problem with subscription handling

Signed-off-by: gkatsikas <katsikas.gp@gmail.com>