cleaned up function interface to avoid referencing the file system in the worker functions.
replaced StringTable's operators with functions.. The main reason is that these are far easier to look up when browsing the source.
This also fixes a premature translation in SBARINFO that was done in the parsing stage, not the printing stage.
* making all members protected (but adding friend overrides for the classes which still need it)
* allowing to read data without retrieving the FResourceLump object.
* use a different subfolder for each IWAD's saves.
* do not allow load and save CCMDs to escape the save folder. Absolute paths and '..' are being blocked now.
* unified savegame path and filename generation in one single function. All ad-hoc file name generation was replaced.
* -loadgame will also use the designated savegame folder now.
