[RCD-37] ChangeLog: address PR entries assigned to me
[RCD-37] ChangeLog: address PR entries assigned to me

These were all backport PRs, so ChangeLog entries were already written
for the previous version.

input-output-hk/pos-haskell-prototype,input-output-hk/cardano-sl,input-output-hk/cardano-sl,input-output-hk/pos-haskell-prototype,input-output-hk/pos-haskell-prototype,input-output-hk/cardano-sl,input-output-hk/cardano-sl