Adding Remote Spark Client. Following changes have been added:
* Pulled in Remote Spark Client.
* Removed Logback dependency from Livy and standardized on slf4j.
* Added a new class that can be used to track sessions and their clients. It times out sessions and can use them to submit jobs from the servlet.

Todo, here or in a followup PR:
- Harmozine dependencies, including Spark
- Change configs from `hive.spark` to `livy.`
48 files changed