Add logViolationCountToConsole property

The plugin is missing a property to allow users to log the violation count to console.

There are already a couple of places where the violation count may be logged, but it doesn't happen unconditionally. The DefaultCheckstyleExecutor may log the error count, but only if there are error-severity violations. The CheckstyleViolationCheckMojo.countViolations method may log the violation count, but only if there are ignored violations.

It would be nice if a logViolationCountToConsole property were added. Printing the violation count is convenient in cases where e.g. you have fixed some violations in a project and now want to reduce maxAllowedViolations. Currently you have to either manually count the violations from the report, or set maxAllowedViolations to 0 to get the plugin to fail and print the violation count.