EMI: A first set of patches to improve Mac-support (German only)

This adds:
* Specific detection of the German version of EMI
* MD5 check for "EFMI Installer", which is necessary for the mac version
* A mention in the readme file that the EFMI Installer file is needed.
* Loading "EFMI Installer" if it exists (there already is code that loads "Monkey Island 4 Installer", but the german version had a different filename. This specific change does not check which language version the game has, and we are likely to need to check the various versions of the game to know which file we need.

This does not fix the issue that local.m4b should be cached in memory, as the continuous reloading of this file is expensive when getting it from the .sit decoder every time.