This add a system for adding generic instances of the DynamicSEXP class
to the SEXP system. The only implementation at the moment is the LuaSEXP
which is used by the mn.addSEXP lua API to allow Lua to add new SEXPs.
Since this requires that FRED also runs lua scripts I added a mod table
option to enable scripting in FRED. Since the current scripts are not
built with FRED in mind it would likely break all these scripts if FRED
would be opened with normal scripting enabled.
This fixes#1320.
