Prepend Maven central in the pluginRepositories block

This should decrease the burden on our artifactory to resolve external
dependencies in the Travis builds.
Prepend formats-common repositories with Maven Central (seralizer, xalan...)
Prepend autogen/pom.xml with Maven Central (velocity)
Prepend format-bsd/pom.xml repositories with Maven Central (perf4j)
Prepend formats-gpl/pom.xml repositories with unidata (netcdf)
Remove duplicate repository and prepend with ome.external (JWlz)
merge dev_5_0 -D org: PR 1231 (Update version history for 5.0.3)
merge dev_5_0 -D org: PR 1236 (Prepend Maven central in the pluginRepositories block)
merge dev_5_0 -D org

Repository: openmicroscopy/bioformats
Excluded PRs:
  # PR 1230 melissalinkert 'Update version numbers to 5.0.3' (label: exclude)
  # PR 1223 melissalinkert 'Ask Travis to retry failed builds' (status: error)
Already up-to-date.

Merged PRs:
  # PR 1231 melissalinkert 'Update version history for 5.0.3'
  # PR 1236 sbesson 'Prepend Maven central in the pluginRepositories block'

Generated by OME-5.0-merge-push#138 (http://ci.openmicroscopy.org/job/OME-5.0-merge-push/138/)