Make sure log levels in logging servlet can also be set by a GET request instead of only POST

Since CMS7-7698, you can only POST a request to change the log levels. It has now become unnecessary cumbersome to set the log-level of a package to something else, for example

http://localhost:8080/cms/logging/?ll=org.hippoecm.hst.core:WARN

should be enough to set the entire 'org.hippoecm.hst.core' pacakge to log level WARN. Since this now must be a post, it is unnecessary complex to achieve