updated sdl and lowered minimum ios to 3.0

As sheepluva pointed out, allowing this message to be legal allows naughtiness. The server usage of this message does not seem to use this check.

remove any thread-safe stuff I introduced since it's not needed as unC0Rr pointed out it's not needed, we are single-threaded (thanks :D) from what I understood this time, Qt is clever enough to sequentialize all events and child destructions instead of spawning threads also some docs/comments

Fix for 'The "optimized" argument must be followed by a library.' cmake failure

adding simple doc build script

this should fix stylesheet importing on windows, but we'll see

fix of /saveStyleSheet command, error message on stylesheet import fail

tweak and document abstract page

on file save: create parent directories if needed

unbreak command auto-completion (was broken since r0b92341adb6a - 52 commits ago)