upgrade to checkstyle 8.0

[romani]

http://checkstyle.sourceforge.net/releasenotes.html#Release_8.0 ,
upgrade version at https://github.com/checkstyle/sonar-checkstyle/edit/master/pom.xml#L88

Migration notes:
If EmptyBlock Check was used with option='stmt', after update plugin there will be an error like:
[ERROR] Failed to execute goal org.sonarsource.scanner.maven:sonar-maven-plugin:3.2:sonar (default-cli) on project checkstyle-sonar-plugin-parent: Can not execute Checkstyle: cannot initialize module TreeWalker - Cannot set property 'option' to 'stmt' in module EmptyBlock: InvocationTargetException: unable to parse stmt: No enum constant com.puppycrawl.tools.checkstyle.checks.blocks.BlockOption.STMT -> [Help 1]
To fix problem set option=statement

[romani]

MethodCountCheck: add ANNOTATION_DEF to toknes to avoid NPE

updated

api changes: make getAcceptableTokens/getRequiredTokens/getDefaultTokens methods as abstract in Check.java.
deprecate Checker.setClassloader , replace with Checker.setClassLoader.
Remove deprecated Check class.
CheckstyleAntTask: substitude setConfig(File) with setConfig(String).
remove deprecated getFilename menthod from FileContents

not affected.

rename STMT in BlockOption class to STATEMENT

updated

Remove unnecessary text from Javadoc tokens
Cache conflict between Maven/Ant and Eclipse/CLI run

not affected.