Reorganized configuration an APIContext.

1. Fixed a few bugs (not actually getting the ISteamUnifiedMessages,
for example).
2. Added a prep(int appid) function to actually configure the Context.
3. Added some more error checking in Context while at it.
4. Some syntax/minor fixes.
Grammer fix.

1. Also forgot to mention added directory+hardcoded filenames for
configuration and app version DB.