build: Move & tweak m-compiler-p config.
build: Move plugin config to pluginManagement.
build: Update some plugins.
build: Disable fork in findbugs-m-p.
build: Remove empty findbugs-exclude.xml.
build: Move checkstyle config to src/conf.
build: Update Guava to v17, from 14.0.1.
build: Add pitest-maven v0.33.
build: Re-order plugin executions.