upgraded Findbugs, Checkstyle and PMD

- removed pmd library: now it is loaded from maven repo
- added pmd-java library into build.gradle so java rules are taken from repo not local custom jar
- upgraded Findbugs, Checkstyle and PMD, resolved problem with dependencies
- minor changes required by new PMD API
- better support in case when findbugs throws exception when there is no file for analyzing
Are you going to merge this patch or shall I keep it on my master only?