Make it easy for a Xiana app to turn off logging messages

[soulflyer]

Xiana is "noisy" in apps built using it. It should be easy to turn this off, as we use timbre which can set logging levels. It looks like control of this level is set inside the xiana code but it should be set in the app.

[soulflyer]

Ugh. Looks like we are using both Timbre and Clojure.tools.logging. Should remove one before completing this.

[jiriknesl]

We should absolutely use just 1. Which one do we use more?

[soulflyer]

Actually we only use Timbre, but we are seeing logging from included libraries via clojure.tools.logging. We can arrange for both to be controlled from the config.

[gmsvalente]

• create a function that runs at system config time to set timbre log level