Emi config

This pull request add the support for registry in EMI (Demo and Windows retail version yet).
It's loosely based on Somaen's prototype (https://github.com/somaen/residual/commit/d41d01a11ff513b759c779cca0fc5e69b6a105f8)

It adds a very simplified version of Grim registry, which can be used in Lua script through GetResidualVMPreference and SetResidualVMPreference opcodes.
The configuration table defined in _options.lua, which has been previously loaded and saved by system_prefs.loadprefs and system_prefs.saveprefs, is replaced with a custom tag method, which hooks into registry with the new opcodes. The tag method and its loader, is defined in dists/engine-data/patches/emi/residualvm-prefs.lua.
_options.lua.patchr and _options.lua_1.patchr add code to load this file, respectively for retail and demo version. 

It also add a new patch container (residualvm-emi-patch.m4b), like it has been done for Grim Fandango.