update gradle check task

- move checkstyle and lint config files to new config folder
- remove .checkstyle files, which are only needed for Eclipse
- output folder for lint and checkstyle results set to build/reports
- activate pmd 5.1.1 (gradle 1.12 default is 4.3)
- toolVersion property is deprecated - but haven't found a workaround
- rulesets with excluded rules are moved to specific
ruleset files containing only one ruleset.
one general ruleset file did not work - excluded rules were ignored.
see http://stackoverflow.com/a/23546851/2093483
- gradle check task now executes pmd as well