first commit
execute sql query and return result set as vector<map<string, string>>
remove SqlHelper::executeQuery(string sql, vector<string> fields)
execute sql from client's request and get result set as vector<map<string, string>>

add SqlListener::onReceive()
rename SqlListener::run() to completionLoop()
convert result to json and return to client
add config file and settings dialog
update logging checkbox state by loading config file
write config file whenever logging checkbox state changed
use append mode for log file writing
SqlListener push client's sql request to queue, and then Worker will process the requests queue
update conns_count when a connection is created or lost
validate sql
add SqlListener::closeConnection()
display connections count in main window
fixed that before worker process a request, the request may be freed when client disconnects
use shared_ptr between SqlListener and Worker
Add SqlListener::resources to manage resources (SocketState*), when its ref count reaches 0, the resource will be freed.
Add Visual Leak Detector
embed python to check whether sql is valid
extract method updateToSendListCount
Merge branch 'master' of https://github.com/gbstack/dbclient

Conflicts:
	.gitignore