Rewrite initialisation to not restart process

[fkaa]

Not bulletproofed 100%, but should be good enough for dev.

• Changed the boot mode enums to not be "handwritten"
• Merged IB_LAUNCHER to be IB_CLIENT | IB_SERVER for now as mentioned by @rakiru
• Instead of restarting the process, there's now a global quitflag which can either be:
  • 0 – Game should not quit
  • IB_QUIT_SHUTDOWN – Game should quit
  • IB_QUIT_RESTART – Game should go through all de-inits, set up the appropriate globals, and call the inits again.
• The quitflag is checked in a loop and quitting is deferred to the end of a frame
• Two new lua functions to interact with the new system:
  • C: icelua_fn_client_create_server
  • Lua: client.create_server(port, basedir)
  • C: icelua_fn_client_join_server
  • Lua: client.join_server(port, address)
• These two functions simply set the quitflag (and a bit of cleaning up globals) and does not block execution after they are run.
• Both functions are only available in #ifndef DEDI

[rakiru]

Launcher should be its own flag too. Being both client and server is possible withotu also being the launcher (-s mode). It should be (0x4 | IB_CLIENT | IB_SERVER). Launcher mode gives a lot of access to things that -s mode doesn't need.

Edit: It's less of a mode on its own and more of a "can access anything" flag. Perhaps leaving it just as 0x4 and renaming it to IB_LOCAL or IB_FULLACCESS would make more sense.

[rakiru]

Launcher doesn't need port parameter, it can just default to 0.

[rakiru]

There may be some memory leaks or something, but the Lua state(s) at the very least are destroyed, so we should be good for now.