- Restored execute permissions

- Added/Updated headers
- Added script to update copyright headers

- 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

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>