Added customizable command log format (Date+Time are now available)

Added the option format to config files (config.yml + worldedit.properties). By default, current date and time are displayed.
The formatting function is implemented by analogy with the class java.util.logging.SimpleFormatter

worldedit-bukkit/src/main/resources/defaults/config.yml

@@ -40,6 +40,17 @@ use-inventory:
 logging:
     log-commands: false
     file: worldedit.log
+    # The format of custom log message. This is java general format string (java.util.Formatter). Arguments are:
+    #   1$ : date - a Date object representing event time of the log record.
+    #   2$ : source - a string representing the caller, if available; otherwise, the logger's name.
+    #   3$ : logger - the logger's name.
+    #   4$ : level - the log level.
+    #   5$ : message - the formatted log message returned from the Formatter.formatMessage(LogRecord) method. It uses java.text formatting and does not use the java.util.Formatter format argument.
+    #   6$ : thrown - a string representing the throwable associated with the log record and its backtrace beginning with a newline character, if any; otherwise, an empty string.
+    # For details see:
+    #   https://docs.oracle.com/javase/8/docs/api/java/util/Formatter.html
+    #   https://docs.oracle.com/javase/8/docs/api/java/util/logging/SimpleFormatter.html#format-java.util.logging.LogRecord-
+    format: "[%1$tY-%1$tm-%1$td %1$tH:%1$tM:%1$tS %4$s]: %5$s%6$s%n"
 
 super-pickaxe:
     drop-items: true