Remove unused exit codes
Minor changes to the startup and shutdown code

- Update comments
- Close logs in LogManager destructor instead of relying on other code to do it
- Change return type of InspIRCd::Run() to void
- private: InspIRCd::CheckRoot()
- Change log message type of setgroups() etc. errors to "STARTUP"
- Load cmd_privmsg in PURE_STATIC builds
Cleanup of the InspIRCd and CommandParser classes and typedefs.h

Removed functions:

InspIRCd:
- Restart() - unused
- DoSocketTimeouts() - no implementation exists
- AddCommand() - useless wrapper around ModuleManager::AddService()

CommandParser:
- IsValidCommand() - unused
- ProcessParameters() - no implementation exists