Issue #3301573 by catch, ravi.shankar, mrinalini9, mherchel, lauriii, alexpott, nod_, acbramley, nsciacca, kevinquillen, Chi: Remove the aggregate stale file threshold and state entry

Issue #1014086 by catch, nod_, martin107, quietone, dww, mariacha1, Spokje, yogeshmpawar, pounard, Wim Leers, mfer, mikeytown2, mbutcher, moshe weitzman, Fabianx, borisson_, alexpott, donquixote, sun, andypost, dawehner: Stampedes and cold cache performance issues with css/js aggregation

Issue #2665992 by alexpott, klausi, heykarthikwithu, xjm, tstoeckler: @file is not required for classes, interfaces and traits

Issue #2307419 by Wim Leers: AssetCollectionOptimizerInterface should allow listing and deleting all aggregates (optimized collection assets).

Issue #352951 by Wim Leers, mfer, mcjim, larowlan, RobLoach, sdboyer, Owen Barton, JohnAlbin: Make JS & CSS Preprocessing Pluggable.