[maven-release-plugin] prepare release 2.1-beta1

git-svn-id: https://languagetool.svn.sourceforge.net/svnroot/languagetool/trunk/languagetool@9571 2fe6a88b-1217-0410-b804-ba6ed01314b8
[maven-release-plugin] prepare for next development iteration

git-svn-id: https://languagetool.svn.sourceforge.net/svnroot/languagetool/trunk/languagetool@9573 2fe6a88b-1217-0410-b804-ba6ed01314b8