This PR enables auth cookies to be used simultaneously with plaintext paasswords sent in the cookie authID field.
* Hoist a bunch of checks from the login packet handler into helper functions.
* Rename the LoginType enum to AuthMethod and distinguish it from the iLoginType packet field (see comment in code for why these should be decoupled).
* If the provided token does not pass the cookie check and password auth is enabled, treat it as a plaintext password and authenticate if it is correct.
* Auth cookie support
* Add config option for auth cookie support
* Safe handling of TEGid/auth_id strings
* Fix bad size calculation due to pointer cast
* Expiration timestamp instead of valid bit
* Change setting to "allowed auth methods"
This allows plaintext password auth to be disabled altogether
* PR feedback
* Database.hpp is still the only external include file (moved to db/)
* The header is still uppercase to match its namespace
* db/internal.hpp is the shared header for the DB source files
* Added -Isrc/ compile flag for src-relative include paths
* Hoisted CHDR above CSRC in Makefile (it was bothering me)
* make clean now removes all objects in the subdirectories as well
