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
* use smart pointers for almost all widget fields
* use SDL2 texture for cursor
* a lot af small tweaks and formatting
* removed CompImage class, it is actually useless as long as regular SDLImage support margins
* CGuiHandler: use smart pointers for [push|pop]Int
We need to make sure it's not stay active during gameplay.
Proper fix would require actually removing menu interface from GH, but then GH needs refactoring too.
* Changed most gui classes to use shared pointers
* Store and use IImage as shared_ptr
* CSpellWindow redesign
* AdventureMapClasses cleanup
* CLabel: store background as smart pointer
* Store CObjectList items as smart pointers
* Removed destroy function of list item
* Store toggle buttons as smart pointers
* Use CComponent as smart pointer
* Attempt to fix artifact merchant drawing
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.
