This commit provides support for automated invokation
of the ztpUpdate RPC upon a DEVICE_UPDATED event.
When this event is triggered, the Automation component
fetches the associated device configuration and applies
it to the device.

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

Common:
- Extended context proto with 2 methods: UnsetService and UnsetSlice

Context component:
- Added timestamp to logs
- Added methods UnsetService and UnsetSlice to Context client
- Implemented methods UnsetService and UnsetSlice in Context servicer
- Resolved conflict between service and slice entities with constraints and configrules

Common:
- temporarily added backend to pathcomp service for debug purposes

Proto:
- Added KDisjointPath Algorithm to pathcomp proto

Frontend:
- refactored Servicer to cope with multiple algorithms
- added implementation of ShortestPath algorithm
- added implementation of KShortestPath algorithm
- added implementation of KDisjointPath algorithm (partial)
- moved PathComp servicer tools to algorithms subfolder
- added new unitary test scenario (DC's with CellSiteGWs and Transport Network) to validate KDisjointPath algorithm

- Slice: added config rules
- Added EndpointPriority constraint
- Modified IsolationLevel constraint to contain a repetition of items

- Arranged commit before merge
- Replaced string-based timestamps by context.Timestamp
- Created helper functions to convert timestamps string from/to float
- Arranged requirements to meet dependencies of converter functions

- Arranged .gitignore & .gitkeep files in common proto folder
- Created specific run_tests_locally script for Context component
- Moved imports from *.proto folder to common.proto folder
- Adapted common.tools.object_factory to new proto definitions for ConfigRule and Constraint
- Extended common.tools.type_checkers to new proto definitions for ConfigRule and Constraint
- Removed context's genproto.sh script
- Adapted Events generated to new timestamp data type
- Minor code and linting fixing

- fixed issue with messages in policy.proto and context-policy.proto
- modified and unified script to generate Python code from proto files
- segregated script to generate UML code
- added/modified apropriate .gitignore files to prevent uploading generated code. It should be generated locally or during creation of Docker containers
- added symbolic link from common/proto to folder containing python generated code

PolicyAdd rpc replaced by PolicyAddService & PolicyAddDevice