* Move client list to ServerEnvironment and use RemotePlayer members instead of Player
* ClientEnvironment only use setLocalPlayer to specify the current player
* Remove ClientEnvironment dead code on player list (in fact other players are CAO not Player objects)
* Drop LocalPlayer::getPlayer(xxx) functions which aren't used.
* Improve a little bit performance by using const ref list for ClientEnvironment::getPlayerNames() & Client::getConnectedPlayerNames()
* Drop isLocal() function from (Local)Player which is not needed anymore because of previous changes

This change permits to cleanup shared client list which is very old code.
ClientEnvironment doesn't use player list anymore, it only contains the local player, as addPlayer is only called from Client constructor client side.
Clients are only CAO on client side, this cleanup permit to remove confusion about player list.

* remove IGameDef from Player class, only LocalPlayer has it now
* move many attributes/functions only used by LocalPlayer from Player to LocalPlayer
* move many attributes/functions only used by RemotePlayer from Player to RemotePlayer
* make some functions const
* hudGetHotbarSelectedImage now returns const ref
* RemotePlayer getHotbarSelectedImage now returns const ref
* various code style fixes

* ClientEnvironment now uses UNORDERED MAP for active objects
* Use RemotePlayer and LocalPlayer everywhere it's possible
* Minor code style fixes
* Drop Client::getBreath() unused function

* Server/Client Environments now have an helper to cast Player object in the right type to use it
* Server: use RemotePlayer everywhere and remove previous added casts
* Client: use LocalPlayer where needed
* Environment: remove unused functions (getPlayers(), getRandomConnectedPlayer(), getNearestConnectedPlayer())

Speed up emerge thread by using unordered map in a few places. Looking at 25% speedup in Emerge thread on Just Test.

* LocalPlayer take ownership of maxHudId as it's the only caller
* RemotePlayer take ownership of day night ratio as it's the only user
* Pass getPlayerControl as const reference to prevent object copy on each call (perf improvement in ObjectRef::l_get_player_control call)
* getPlayerSAO is now only RemotePlayer call
* get/setHotbarItemCount is now RemotePlayer owned
* Server: Use RemotePlayer instead of Player object on concerned call to properly fix the object type
* PlayerSAO now uses RemotePlayer instead of Player because it's only server side
* ObjectRef::getplayer also returns RemotePlayer as it's linked with PlayerSAO

Add missing documentation for 'register_biome' and
'clear_registered_biomes'.
Add documentation for 'nodeupdate_single'. 'nodeupdate'
is not yet documented due to a bug it causes.

	The initial problem was that mutex_auto_lock.h tries to use std::unique_lock<std::mutex>
	despite mutex.h not using C++11's std::mutex on Windows. The problem here is the mismatch
	between C++11 usage conditions of the two headers. This commit moves the decision logic
	to threads.h and makes sure mutex.h, mutex_auto_lock.h and event.h all use the same features.

Also remove some unused parameters/functions

Fixes #4579, a regression introduced by commit

d4c76258 "Chat: new settings to prevent spam"

This is part 2 for 5f084cd9

Other improvements:

* Use the defined ItemGroupList when used
* make Client::checkPrivilege const
* inline some trivial functions
* Add ActiveObjectMap typedef
* Add SettingsEntries typedef

* This permit to improve performance on C++11 builds
* use some existing typedefs in tools maps
* minor code style changes

Added the following chat coreside features
* Chat messages length limit
* Message rate limiting
* Message rate kicking

Note:
* handleChat now takes RemotePlayer pointer instead of u16 to remove useless
  lookups

Remove uses of std::map.
Make sure we use ContentFeatures reference not value.
Original commit by gregorycu.

The fallback vector is in case 'wallmounted to dir' is nil due
to voxelmanip placing a wallmounted node without resetting a
pre-existing param2 value that is out-of-range for wallmounted.
The fallback vector corresponds to param2 = 0.