Add support for java.util.logging

[Riduidel]

I tend to use java.util.logging for logging. Could you add its support ?

[achimgrimm]

I never used java.util.logging. I guess, that makes me to a bad person to implement it. :)
But I like the idea and would be happy to check and changes.

[akutschera]

The PR above will use the existing interface of ExpectedLoggingAssert, i.e. it uses hasErrorMessage when checking for log messages with level "SEVERE", because j.u.l. has no error level.
To stay withing the j.u.l. domain we could add hasSevereMessage with the same functionality as hasErrorMessage.
Using hasErrorMessage to check for a severe message could be confusing to the test reader.
Since I don't use java.util.logging either, @Riduidel , could you help here and say what you would prefer?
Bonus question: Would you remove hasErrorMessage in the assertj-logging-jul artefact?
Of course this goes for all the other methods that handle error/severe levels, too.