Add log4j logging (#383)

Enables java logging. The log level can be changed by setting a variable.
Set and run like this:

export JAVA_OPTS="-Dorg.metafacture.metafix.logLevel=DEBUG"; ./gradlew installDist;  cd metafix-runner/build/install/metafix-runner; bin/metafix-runner $pathTo.flux

Note that you cannot use `./gradlew :metafix-runner:run ...` as setting
the log level only works within the distribztion.

Co-authored-by: Jens Wille <[email protected]>

Author: dr0i

metafix-runner/build.gradle

@@ -39,11 +39,15 @@ dependencies {
 application {
   mainClass = 'org.metafacture.runner.Flux'
 
+  applicationDefaultJvmArgs = [
+    "-Dorg.metafacture.metafix.logLevel=INFO"
+  ]
+
   if (project.hasProperty('profile')) {
     def file = project.getProperty('profile') ?: project.name
     def depth = project.hasProperty('profile.depth') ? project.getProperty('profile.depth') : 8
 
-    applicationDefaultJvmArgs = [
+    applicationDefaultJvmArgs += [
       "-XX:FlightRecorderOptions=stackdepth=${depth}",
       "-XX:StartFlightRecording=dumponexit=true,filename=${file}.jfr,settings=profile"
     ]

metafix/src/main/resources/log4j.xml

@@ -0,0 +1,18 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!DOCTYPE log4j:configuration SYSTEM "http://logging.apache.org/log4j/1.2/apidocs/org/apache/log4j/xml/doc-files/log4j.dtd">
+
+<log4j:configuration>
+    <appender name="stdout" class="org.apache.log4j.ConsoleAppender">
+        <layout class="org.apache.log4j.PatternLayout">
+            <param name="ConversionPattern"
+                value="%-5p [%t] [%c{1}] %m%n" />
+        </layout>
+    </appender>
+
+    <root>
+        <priority value="${org.metafacture.metafix.logLevel}" />
+        <appender-ref ref="stdout" />
+    </root>
+
+</log4j:configuration>
+