Refactor Settings out of Common.h

[jimkoen]

Currently, dealing with TSettings in Common.h is very tedious (for example when wanting to output all settings for flush them, as requested in #158 ). In addition, Settings access is currently not threadsafe, and encapsulation of security related settings (i.e. AuthKey) from the rest of the application is implemented in a crude manner.

Settings need to be refactored into an abstraction that least supports:

• Thread safe access
• Some form of rudimentary support / foresight in implementation to be able to handle them from within the Lua interpreter
• Masking individual settings from parts of the application for security reasons

[jimkoen]

Closed, was fixed in #295