* Move networkcode to a dedicated directory
* Rename clientserver.h to network/networkprotocol.h (Better name) and sanitize some includes
* Create object NetworkPacket
  * It stores command (opcode) and data separated
  * It also stores peer_id
  * Data reading can be done by using a streaming interface
* Change packet routing analysis
  * Remove old conditional analysis
  * Now uses function pointed analysis and add connection state ({Client,Server}::handlers)
  * Connection state permit to categorize condition to handle before analyze packets
  * Create a handler for depreciated messages, instead of duplicating code

Conf.example: Add mgv7 cave1, cave2 noiseparams
Mgv7: Make skipping of mountain code relative to y=0 not water level
Mountain noise offset now -0.6 to compensate
Tune chance of large caves

Remove software exception translator function, simplifying exception handler
macros.  FatalSystemExceptions are left unhandled.

Remove inventorycube() workaround for default:glass in minimal game

Disables local map saving for all local server types

See: https://github.com/minetest/minetest/issues/2024

This fixes issue #2219

When SER_FMT_VER_LOWEST is set to zero, then the test is stupid in INIT because all client works. In mapblock we check if client's serialization version is < 24, but if client sent serialization version < 24 (15 for example) the server set it and tried to send nodes, then BOOM

To resolve the problem:
* Create a different CLIENT_MIN_VERSION to handle this problem
* Remove the exception
* Use an assert in case of bad developer code

A missing map_meta.txt should be treated simply as if there were a blank file.

Revert "Fix a crash (assert) when client set serial version < 24 in INIT command SER_FMT_VER_LOWEST is set to zero, then the test is stupid in INIT because all client works. In mapblock we check if client's serialization version is < 24, but if client sent serialization version < 24 (15 for example) the server set it and tried to send nodes, then BOOM"

nerzhul is (may?) be working on a new solution. For the moment this is reverted because old worlds cannot be loaded (see discussion on github for the commit).

This reverts commit 800d1927.

Settings fixes Make the GameGlobalShaderConstantSetter use the settings callback (8% perf improvement in game loop) Ensure variable is set Ensure settings callback is threadsafe

Revert "Make the GameGlobalShaderConstantSetter use the settings callback (8% perf improvement in game loop)"

This reverts commit a555e2d9.

Fix a crash (assert) when client set serial version < 24 in INIT command SER_FMT_VER_LOWEST is set to zero, then the test is stupid in INIT because all client works. In mapblock we check if client's serialization version is < 24, but if client sent serialization version < 24 (15 for example) the server set it and tried to send nodes, then BOOM

Make the GameGlobalShaderConstantSetter use the settings callback (8% perf improvement in game loop)
Amend the settings callback to support userdata