- Merged logics to manage composition of config rules

bug fix: temporary fix for MEC PoC demo. Config rules and OpenConfig driver for L3VPN should change based on telefonica recipe.

- Added method generate_neighbor_endpoint_config_rules to compose config rules for neighbor endpoints

- Extended ComposeConfigRules to propagate static routes in L3 services
- Extended ComposeConfigRules to recognize custom config rules with the form /device[]/endpoint[]/vlan[]/settings

- Added composition of device-specific config rules

- Corrected endpoint-to-link datastructure
- Improved identification of config rules by device/endpoint uuid/name
- Assumed links are unidirectional
- Rewritten sub-serice computation logic to consider intermediate controllers
- Rewritten method eropath_to_hops based on new endpoint-to-link datastructure
- Minor bug resolutions
- Updated test pathcomp temporary code

- Added logic to ignore mgmt-related links
- Improved composition of subservice config rules
- Cleaned up Constants
- Updated sub-service computation logic