[refactor] New buff framework (player implementation)

Get rid of `iConditionBitFlag` in favor of a system of individual buff
objects that get composited to a bitflag on-the-fly.
Buff objects can have callbacks for application, expiration, and tick,
making them pretty flexible. Scripting languages can eventually use
these for custom behavior, too.

TODO:
- Get rid of bitflag in BaseNPC
- Apply buffs from passive nano powers
- Apply buffs from active nano powers
- Move eggs to new system
- ???

Makefile

@@ -50,6 +50,7 @@ CXXSRC=\
 	src/db/email.cpp\
 	src/sandbox/seccomp.cpp\
 	src/sandbox/openbsd.cpp\
+	src/Buffs.cpp\
 	src/Chat.cpp\
 	src/CustomCommands.cpp\
 	src/Entities.cpp\
@@ -96,6 +97,7 @@ CXXHDR=\
 	vendor/JSON.hpp\
 	vendor/INIReader.hpp\
 	vendor/JSON.hpp\
+	src/Buffs.hpp\
 	src/Chat.hpp\
 	src/CustomCommands.hpp\
 	src/Entities.hpp\