Restructure Allen sources and CMake
Allen is using a source tree layout and a corresponding CMake configuration that evolved organically and was never aligned with the modern cmake used in other LHCb projects.
This leads to issues and it would be beneficial to restructure it. Building in "standalone" mode needs to be considered.
lb-dev currently doesn't work for Allen. Beyond CMake include issues, lb-dev relies on the fact that a shared library or python module can be replaced on a per-package level. This will not work without a significant overhaul of the CMake, because Allen currently builds all device code into a single project-wide shared library (libAllenLib.so).
Edited by Roel Aaij