Add query and task monitoring feature

[taewhi]

The status and statistics have to be monitored by queries and execution tasks.
Some information on performance could be recorded to log files or catalog tables.

[taewhi]

This feature has been implemented at ef3cf2c .
This option is turned off by default, since 64affb3 .
It can be turned on by setting the following parameters in traindb.properties:

traindb.server.querylog=true
traindb.server.tasktrace=true