Added Logging

Added logback as a logging implementation for SLF4J with Scala wrapper provided by Grizzled.
http://software.clapper.org/grizzled-slf4j/

In most cases it should be sufficient to extend `grizzled.slf4j.Logging` and use the `error`, `debug`,`info` methods.

This will require the following Pull Request ion GT to be merged to function:
https://github.com/geotrellis/geotrellis/pull/883