CGE2: Add, implement and use saveHeroPos().
CGE2: Heavily rework memory management of Sprites.

Hopefully it will solve a bunch of memory leak problems.
Now Spare is a central container, which stores pointers to every Sprite currently used by the engine.
Because of that, there's no more need for Queue's clear().
In case of snKill(), it's just a safeguard, since it's only used by the engine to "kill" the speech bubbles, but we will check Spare anyway, so it's the safest this way.
CGE2: Silence warning.
CGE2: Partially working save/load system.

There's a mayor bug which blocks the toolbar from interaction after loading. To be investigated during the upcoming days.
CGE2: Remove unnecessary parameter from Spare::sync().
CGE2: Rename saveHeroPos() to storeHeroPos().
CGE2: Rename and heavily rework Bitmap::forceExt().

Since the extension is always ".VBM" in case of Bitmaps, there's no need to pass it as an argument.