Moar filtering!

[jhannes]

• ConditionalLogEventFilter should generate a ConditionalLogEventGenerator to avoid generating logevents that will be filtered out
• Rename LogEventPredicate to LogEventCondition?
• Replace logic in AbstractFilteredLogEventObserver with LogEventConditions
• Create MDC based filters. E.g. observer....requireMdc.user=admin|tester and observer....suppressMdc.path=/status
• Combine filters on (single observer) and ConditionalLogEventGenerator?