LogMessage: Check type of log_message

This includes very minor other changes.
LogPrinter: Rename log_message parameter to message

In those cases the given thing is a string instead of a LogMessage. We
should name it appropriately.
LogPrinter: Pass timestamp like it should

A usual stupid bug.
LogPrinter: Return in specialized cases too
LogPrinterTest: Adapt testcases to new API
helpers: Add RESULT_SEVERITY
helpers: Add Result
output: Add Outputter
output: Add ConsoleOutputter
ANALYSER_KIND: Strip useless UNKNOWN kind
Analyser: Return value returned by run_analyser
Analyser: Codestyle fix
analysers: Add GlobalAnalyser
analysers: Add LocalAnalyser
analysers: Add GlobalAnalyserTest
analysers: Add LocalAnalyserTest
StringConverter: Strip comment down to relevant part