Fixed console errors for failed parent dependencies of default groups that already exist caused by fb11729547 consistency fixes
Made GroupManager.groups readonly to discourage overwriting it. Could still do with better encapsulation to prevent consistency problems if modified externally.
Added UpdateGroup method to GroupManager
Refactored Group handling of permissions and chatcolor to prevent inconsistent data
Notably:-
* AddPermission now does the right thing when passed the string "!permission"
* Converted ChatColor from method to getter / setter
Added RemovePermission to Group
Refactored GroupManager Permissions handling to ensure consistent data between DB and internal objects
Removed redundent AddGroup method in preference to a default value on the main method
Correct some tabs vs spaces
Added ParentName helper to Group
Fixed inverted parameters to error "Invalid parent {0} for group {1}"
Server Side Inventory security improvements, blocking trashcan and "banks" items
CovertCorruption is now more thorough.
PvP Modes, normal, always, disabled now configurable
Initial group prefix/suffix implementation
Range checks reworked, Killing ice blocks now ignored for ice rod.
Adding a NPC name to item banlist will block it from spawning
Added configs to disable snowballs and clown bombs from npcs.
