minor docfixes in ClusterSingletonManager.scala
=tes #15155 prettyduration should work with infinity
adjust default precision to be 4 (fits use case better)
=act #13964 make BalancingPool mailbox configurable
=doc #15160 Minor spelling, wording and grammar fixes.
Merge pull request #15160 from ectsue/patch-1

=doc #15160 Minor spelling, wording and grammar fixes.
Merge pull request #2127 from dormidon/3964-unable-to-configure-mailbox-for-routees-under-balancingpool-in-akka-2-3-1

Mailbox configuration for routees under BalancingPool - Issue 3964 fix
Merge pull request #15134 from shikhar/patch-1

minor docfixes in ClusterSingletonManager.scala
Merge pull request #15156 from ktoso/tes-pretty-duration-inf

=tes #15155 prettyduration should work with infinity