Fix policy-related proto issues, unify in a single folder generated code for the different languages, and adapt generation scripts

See merge request teraflow-h2020/controller!124

- 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

Preliminary non-functional version of PathComp component

See merge request teraflow-h2020/controller!123

Multiple small improvements and bug fixes in WebUI

See merge request teraflow-h2020/controller!119

Extended Proto files:

See merge request teraflow-h2020/controller!122

Policy/update policy domain objects

See merge request teraflow-h2020/controller!116

chore(automation): update gRPC port name to grpc

See merge request teraflow-h2020/controller!121

chore(policy): update policy gRPC port name to grpc

See merge request teraflow-h2020/controller!120

- removed hardcoded paths and replaced by url_for methods
- arranged service paths to be homogeneous with other entities
- implemented service delete
- adapted JavaScript scripts to use dynamically generated paths from Jinja
- corrected error logger in delete of device and service
- implemented logic to support deploying the WebUI on a subpath of WSGI servers

chore(automation): change gRPC port to 5050

See merge request teraflow-h2020/controller!118

chore(policy): change gRPC port to 6060

See merge request teraflow-h2020/controller!117

refactor(policy): update policy.proto

See merge request teraflow-h2020/controller!115

PolicyAdd rpc replaced by PolicyAddService & PolicyAddDevice