This commit modifies the liquid transforming procedure to light and
unlight nodes instead of whole map blocks.

This commit rewrites the procedure that is responsible for light
updating.

this commit
-provides iterative solutions for unlighting and light spreading
-introduces a new priority queue-like container for the iteration
-creates per-node MapBlock caching to reduce retrieving MapBlocks from
the map
-calculates with map block positions and in-block relative node
coordinates
-skips light updating if it is not necessary since the node's new light
will be the same as its old light was

This solves the problem whith building where build fails if the libaries have different names.

Flash alpha maximum is reduced from 180 to 127 to avoid player blindness
in combat. Flash alpha minimum is unchanged.
The 'damage_flash' value is now limited to max alpha, to avoid multiple
hits creating a huge value that causes flash to stay at maximum alpha
for a long period. Now alpha always starts to fade immediately after
taking damage.
Both problems can be seen in Minetest let's play videos.
Simplify and optimise some code.

Move static object storage force-delete message from errorstream to
warningstream.
Increase 'max objects per block' setting to 64.
Add missing spaces in warning code.

Rename "refresh" to "processInitData"

Modification of the emergeblocks internal state was not protected
by a lock, causing a race condition.
This can be reproduced by repeatedly running emergeblocks for an
already-generated section of the map (with multiple emerge threads).

	These methods do not actually fail but instead clear the item stack
	and return false if a value like e.g. "" is passed.

* 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())