Adds a multiplayer tab to allow hosting and joining games from within the GZDoom launcher rather than needed to use the command line. This has its own set of defaults independent from the main play page which necessitated rewriting how this information is passed and stored in the backend. A startup info struct is now passed back which has its defaults set from the cvars and then propagates any changes to it back to the defaults after selection is complete, making it much simpler to interface with the engine defaults.
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.
