Exclude commons-logging to the extent that even Gradle’s happy

Gradle hasn’t different exclusion semantics to Maven. In Maven you can
exclude spring-core’s commons-logging dependency once and it’ll be
honoured even if you have multiple transitive routes to commons-logging
via spring-core. In Gradle you have to exclude commons-logging from
everything that has a transitive spring-core dependency. To make matters
worse this doesn’t only apply to dependencies and exclusions declared in
build.gradle but also to dependencies and exclusions declared in the pom
files of the artifacts that a Gradle build depends upon.

In short, to make our starters work as intended with Gradle, this commit
adds many, many exclusions for commons-logging. It also removes
commons-logging exclusions from spring-boot-dependencies’
<dependencyManagement> as they have no effect with Gradle and their
presence can cause us to miss required exclusions in a starter

Fixes #987