Re-organising AdePT as a library

Common headers are now in the AdePT/ directory
Elements independent from AdePT but re-used across examples are now in /examples/common
Adding new Example1, which links against the AdePT library, and contains only user-defined code which AdePT doesn't depend on
- Example1 is based on the custom Tracking Manager integration strategy previously used in the legacy example 22
- The custom Tracking Manager now allows to do region-based GPU tracking
Removed most legacy examples
Exporting three new libraries, AdePT, AdePT_cuda and AdePT_G4_integration
CopCore is no longer an internal package and the library is also exported as AdePT::CopCore
The AdePT core library doesn't depend on Geant4, only AdePT_G4_integration does
G4HepEM is now an external dependency
Adding time information in the AdePT Tracks, to be validated
General cleanup

apt-sim / AdePT