Move LogLevel enum from filelogger to logger.
Move LogHeader to LogStream.
Purge a ton of code related to non <log> related logging.

- InspIRCd::OpenLog
- ./inspircd --logfile [file]
- ./inspircd --nolog

This is no longer needed now we have (since 1.2) custom logging.
Add ConsoleLogStream and modify the debug logging to use it.
Purge FileWriter in favour of std::ofstream.
Purge the old chanlog code from the module file.
Accept a LogLevel instead of an int in logging methods.