Secure session tokens format (#4963)

[gesior]

This PR is based on #4958 , because without it, it was very hard to test build-in HTTP server.

TODO

• decide, if it's fine, that class SessionToken is in game.cpp / game.h - should it be moved to separate files sessiontoken.cpp and sessiontoken.h?
• add migration that drops sessions table in database

Changes Proposed

Replace current TFS session tokens algorithm with new version that:

• does not use database
• detects when password to account changes
• has optional IP validation (default false, in config.lua: sessionTokenIpVerification = false)
• has configurable expiration time (default 30 days, in config.lua: sessionTokenExpirationTime = 30 * 24 * 3600)
• uses SHA-256 sign to detect token modification with configurable secret sign key (default "" [empty string], in config.lua: sessionTokenSecretKey = "")
• works with PHP acc. makers (MyAAC, login.php that works with MyAAC: https://gist.github.com/gesior/6fb7e194a1aedb7980e98399bcca628d ) - I will make PR to MyAAC after this PR is merged into TFS