Add tags to PlayerData + implement a notify-off tag.

Not sure this is that much final, but PlayerData can now carry tags.
NoCheatPlus.sendAdminNotify... will now check PlayerData for the
"notify_off" tag, as a preparation for a command to turn off
notifications.
Put commands on feet.

* Add a new base class for better sub-command handling also for
tab-completion (AbstractCommand).
* Alter package structure slightly, to group command-classes by purpose.
* Some renaming.
[COMMAND CHANGE] Remove delay feature from ncp ban/kick/tell/tempkick.

"ncp delay..." still is available.
Add command to turn notifications off and on again (per player).