Sloved a serious problem in heavily client login-logoff. add a rubbish can, hold sockets to be deleted later

* sloved multi-thread db access problem. the databaseresource class has been
improved, for each thread, a thread-owned db connection will be cloned from main
db connection.

There is still a problem in heavily-test.

const QByteArray & type paras, will cause lift cycle problems. using Value-pass instead.
----
QString, QByteArray supports ref-count and auto-delete , also, these classes support
least-copying, deep-copy will only take place, when the data is about to be changed.
so, in singnals and slots, using QString, QByteArray instead of const QString & and const QByteArray & ,
will not cause performance problem.

Each server instance knows exactly how many clients each server currently have.

It is very strange, that in GNU C++ in Ubuntu, inline-member funcs called by different thread will return zero values.

This svr 2 svr network using zoomPipeline techniques, an Multi-Threads、pipelined dealer.