Introduce AllenOnline

Developments for FEST and HLT1 PRR

• Introduce AllenOnline package
• Move MEPProvider to AllenOnline from Allen
• Adapt to official MEP format
• options for running Allen in Online mode
• Implement MEP input from and MDF output to shared memory buffer manager (MBM)

TODO:

• Use the the 5 most-significant bits instead of the LHCb::RawBank::BankType of the first fragment in an MFP to decide what to do with an MFP. It's probably easiest to include a mapping between LHCb::RawBank::BankType and these bits. An example can be found in Online
• Replace find_package(CUDAToolKit) in AllenOnline with proper propagation of device runtime from the Allen project
• Propage DEVICE_TARGET from Allen

Goes with Allen!650 (merged) Depends on Online!621 (merged)