Apply various customizations to the build

 - update Bintray configuration with additional settings
 - setup metadata required by Gradle Plugin portal
 - apply license, cobertura, findbugs, jdepend and coveralls plugins
 - apply license header to all sources
 - remove unused imports
 - configure metadata for pom generation
 - configure additional Manifest metadata
 - exclude IDEA meta files from git index
 - basic TravisCI setup