- 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

ACL:
- defined generic model for ACLs

Context:
- Extended context.proto with ConnectionSettings
- Extended context.proto with ConfigRules specific for ACLs
Extended context.proto with Constraints for Schedule, Location, and SLAs
- created ContextPolicy to bring persistent storage of policies
- updated genproto.sh

Policy:
- added missing message to list PolicyRuleIds

Policy component's protobufs are updated based upon
the Event Condition Action (ECA) model.
Minor fixes are applied to the slice.proto in order
to compile.

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