Issue #14 : ProxySQL can be started with PROXYSQL START only once

Issue #54 : Implmented a better send_MySQL_OK and implemented send_MySQL_ERR
Fix for issue #52
No resultset was erroneously interpreted as error
Further bug in #14
main() checked GloVars.__cmd_proxysql_nostart instead of GloVars.global.nostart
Fixed this and changed locking logic in Admin
Issue #58
Probably completed
Moved around some code in main (it needs a lot of clean up, it is all test code)
Modules shutdown is performed only if they are active
If GloVars.global.nostart==true , ProxySQL doesn't fully restart even after a PROXYSQL RESTART, it will wait PROXYSQL START

Various bugs/improvements:
- in class MySQL_HostGroups_Handler, use of clear() for vectors MyHostGroups and Servers
- Better implementation of PROXYSQL START (issue #14)