Disabled the following (for MSVC only) that couldn't (or shouldn't) be fixed.
4003: not enough actual parameters for macro 'identifier'
4250: 'class1' : inherits 'class2::member' via dominance
4251: 'type' : class 'type1' needs to have dll-interface to be used by clients of class 'type2'
4275: non dll-interface class 'type1' used as base for dll-interface class 'type2'
Warnings fixes
* Suppress `missing-braces` for Clang
* Fixed many C4275 warnings
* Fixed almost all Clang/GCC warnings
* Silence most frequent MSVC warning.
* Fixed some pessimizing-move warnings
* Fixed some unused capture warnings
New features for players:
* Loading for multiplayer. Any save could be used for multiplayer.
* Restart for multiplayer. All clients will restart together.
* Loading from single save.
* Hotseat mixed with network game. Multiple players per client.
* Now connection to server could be cancelled.
* Return to menu on disconnections instead of crashes.
* Restoring of last selected map, save or campaign on next run.
TLDR on important changes in engine code:
* UI: work with server separated from UI
* UI: all explitic blitting replaced with IntObject's
* UI: all new code use smart pointers instead of DISPOSE
* Gameplay always start through lobby controlled by server.
* Threads receiving netpacks now shared for lobby and gameplay.
* Campaigns: heroes for crossover now serialized as JsonNode.
