Rename some variables in FBAE to improve readability and understanding

[simatic]

Some variables/notions must be renamed in FBAE to improve readability and understanding. For instance:

• Instead of speaking of sites, we should use hosts (because it corresponds to hosts notion in MPI).
• HostTuple ==> Host (same reason)
• AlgoLayer::broadcastersGroup ==> view (notion used in Total Order Broadcast community)
• CommLayer::openDestAndWaitIncomingMsg method ==> CommLayer::execute method (to be consistent with SessionLayer::execute and AlgoLayer::execute