Many small fixes and improvements

• new logo!
• add config value for message
• add support for configuring JSLint
• sputnik now adds comment only once in Stash
• switch to gerrit-rest-java-client library
• bump Checkstyle and CodeNarc versions
• structural refactoring in ReviewFormatter
• skip deleted files while listing files
• fix thrown exceptions when there are no files to review for FindBugs or PMD
• fix NPE when running Sonar