adding syslog appender

This adds support for Syslog as a log destination. You configure it using an OSGi configuration.

![syslog](https://f.cloud.github.com/assets/65906/2167652/9038e15c-951f-11e3-9b53-3811df7ebc49.png)

Tested primarily against https://papertrailapp.com/. When used with papertrail, I'd recommend using
`<appname>: [%thread] %-5level %logger{36} - %msg%n`
as the suffix pattern where `<appname>` is something like "load16" or "devserver". Papertrail gives the first token (up to 36 chars, no whitespace) special meaning.

NOTE: this requires AEM 6.0 Beta and a SNAPSHOT build of Sling Commons Logging, although I fully expect it to work with AEM 6.0 final. The packages are optionally imported, so this has no impact on ACS AEM Commons's usability on 5.6 or 5.6.1