Generate <classname>.cfg/userconfig.cfg files at runtime if they don't exist

 * Closes #87 in conjunction with fortressforever/fortressforever-scripts#3
Did some more research about search paths. They are defined in FileSystem_Steam.dll and set based on gameinfo.txt. Although we can't access the implementation in that dll, there is an analogue (which seems to be accurate) in [public/filesystem_init.cpp](https://github.com/fortressforever/fortressforever/blob/beta/public/filesystem_init.cpp#L498-L590) that's used to compile demoinfo.exe.

Fortress Forever's current search paths:
```
NULL pathID search paths:
c:\program files (x86)\steam\steamapps\common\fortress forever\platform\
c:\program files (x86)\steam\steamapps\common\fortress forever\fortressforever\
c:\program files (x86)\steam\steamapps\common\fortress forever\hl2\
c:\program files (x86)\steam\steamapps\common\fortress forever\platform\config\

GAME search paths:
c:\program files (x86)\steam\steamapps\common\fortress forever\fortressforever\
c:\program files (x86)\steam\steamapps\common\fortress forever\hl2\

MOD search paths:
c:\program files (x86)\steam\steamapps\common\fortress forever\fortressforever\

GAMEBIN search paths:
c:\program files (x86)\steam\steamapps\common\fortress forever\fortressforever\bin\
c:\program files (x86)\steam\steamapps\common\fortress forever\hl2\bin\

PLATFORM search paths:
c:\program files (x86)\steam\steamapps\common\fortress forever\platform\

DEFAULT_WRITE_PATH search paths:
c:\program files (x86)\steam\steamapps\common\fortress forever\fortressforever\
```

The 2013 engine uses search paths to allow customizations to not overwrite files, and instead they'd get loaded from `<gamedir>/custom`. We can sort of do the same thing, but 2013 has a [new implementation](https://github.com/ValveSoftware/source-sdk-2013/blob/55ed12f8d1eb6887d348be03aee5573d44177ffb/mp/src/public/filesystem_init.cpp#L531-L722) that allows it to be less intrusive (we'd have to set fortressforever/custom as the first mod/game path, but then various temp/cfg/etc files get written to it instead of where they should be; 2013 defines custom as a special case using a new wildcard thingy).

This probably isn't the right place to post this, but oh well.