This updates astara-horizon code for the project rename:
* References to Akanda/akanda changed to Astara/astara
* Refernces to RUG/Rug removed or replaced with astara
* RugClient -> AstaraClient
* Panel renamed RUG -> Astara
Also added copyright headers to all code files.
Change-Id: I78eeacda4f8ae16a61890d9cbfd41ddf037b9677
Partially-implements: blueprint astara-horizon-mitaka