Added LogEvent, a class to parse monitoring logs

Just like shinken.misc.perfdata parses perfdata, shinken.misc.logevent parses monitoring logs.

For a given log:
```` 
[1329144231] SERVICE ALERT: dfw01-is02-006;cpu load maui;WARNING;HARD;4;WARNING - load average: 5.04, 4.67, 5.04
````

logevent.data will contain:
````
{
    'alert_type': 'SERVICE',
    'event_type': 'ALERT',
    'service_desc': 'cpu load maui',
    'attempts': 4,
    'state_type': 'HARD',
    'state': 'WARNING',
    'time': 1329144231,
    'output': 'WARNING - load average: 5.04, 4.67, 5.04',
    'hostname': 'dfw01-is02-006'
}
````