kiji-rest: REST-150. Add the slf4j-api and order the classpath deterministically.

Add the slf4j-api in the pom and change the way the classpath is constructed so
that it's a deterministic order of libs specified in the lib/ dir of KijiREST.

Review: https://review.kiji.org/r/2120/
Reviewer: lsheng
commit: https://github.com/kijiproject/kiji-rest/commit/427843ad9bef76ec900c428679d45376b00060cc