classic-ui: fix vulnerability against CSRF attacks CVE-2013-7107 #5346

This is the fix for CVE-2013-7107. From now on the HTTP referer gets
checked if the request of cmd.cgi actually comes from cmd.cgi.
Otherwise the request will be rejected and the user be notified if
possible. Also a new cgi.cfg option "disable_cmd_cgi_csrf_protection"
got added to disable the protection and allow external programs to
submit commands.

refs: #5346
classic-ui: add "current_notification_number" to jsonoutput of hosts and services in status.cgi #5370

new json attribute "current_notification_number" added to host and servcie
status in status.cgi.

refs: #5370
whatthecommit.com: Shovelling coal into the server...
classic-ui: add change entry in Changelog #5346

refs: #5346
Merge branch 'fix/vulnerability-against-CSRF-attacks-5346' into next

Conflicts:
	Changelog

fixes: #5346
Merge branch 'feature/add-notifi-num-to-status-json-5370' into next

fixes: #5370
fixing changelog for last commit