Original commit by t4im, rebased and developed by paramat.
Fix CONTENT_IGNORE being replaced by falling nodes or causing large
areas of sand to collapse into itself.
Format some conditional code for clarity.
Add and clarify some comments.

- interact
- shout
- privs
- basic_privs

This resolves washy font and incorrect mouse handling on Windows if
a screen with high DPI is used.

Replace parameters with the equivalent /Ox

* Separate optional from require dep's in main menu

* Simplify modmgr mod dependency listing code

PlayerSAO::disconnected() function was historical and remove the link between SAO and RemotePlayer session. With previous attributes linked to RemotePlayer saving was working. But now attributes are read from SAO not RemotePlayer and the current serialize function verify SAO exists to save the player attributes.

Because PlayerSAO::disconnected marks playersao for removal, only mark playerSAO for removal and let PlayerSAO::removingFromEnvironment do the correct saving behaviour and all the disconnection process instead of doing a partial removal and let the server loop doing the RemotePlayer cleanup and remove some saved attributes...

Fix for previous commit.

Add minetest.get_server_uptime() function to Lua API

Update lua_api.txt.

* Create UnitSAO, a common part between PlayerSAO & LuaEntitySAO
* Move breath to PlayerSAO & LocalPlayer
* Migrate m_yaw from (Remote)Player & LuaEntitySAO to UnitSAO
* Migrate m_yaw from Player to LocalPlayer for client
* Move some functions outside of player class to PlayerSAO/RemotePlayer or LocalPlayer depending on which class needs it
* Move pitch to LocalPlayer & PlayerSAO
* Move m_position from Player to LocalPlayer
* Move camera_barely_in_ceiling to LocalPlayer as it's used only there
* use PlayerSAO::m_base_position for Server side positions
* remove a unused variable
* ServerActiveObject::setPos now uses const ref
* use ServerEnv::loadPlayer unconditionnaly as it creates RemotePlayer only if it's not already loaded
* Move hp from Player to LocalPlayer
* Move m_hp from LuaEntitySAO to UnitSAO
* Use m_hp from PlayerSAO/UnitSAO instead of RemotePlayer

When rewriting keycode.cpp I overlooked this function, fixes #4683 completely

this should fix #4683

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"