#605 Add custom log levels, create debug logging method

- Log levels in the log file too
- Create migration from old boolean "stop spam" property to new log level property

src/main/java/fr/xephi/authme/output/LogLevel.java

@@ -0,0 +1,38 @@
+package fr.xephi.authme.output;
+
+/**
+ * Log level.
+ */
+public enum LogLevel {
+
+    /** Info: general messages. */
+    INFO(3),
+
+    /** Fine: more detailed messages that may still be interesting to plugin users. */
+    FINE(2),
+
+    /** Debug: very detailed messages for debugging. */
+    DEBUG(1);
+
+    private int value;
+
+    /**
+     * Constructor.
+     *
+     * @param value the log level; the higher the number the more "important" the level.
+     *              A log level enables its number and all above.
+     */
+    LogLevel(int value) {
+        this.value = value;
+    }
+
+    /**
+     * Return whether the current log level includes the given log level.
+     *
+     * @param level the level to process
+     * @return true if the level is enabled, false otherwise
+     */
+    public boolean includes(LogLevel level) {
+        return value <= level.value;
+    }
+}