Tachyon 102 Move logging to SLF4J (with log4j2 as backend implementation)

This PR contains work for sub-tasks under Tachyon-102:
1. TACHYON-107 Update dependencies for SLF4J
2. TACHYON-104 Update logger to use SLF4J
3. TACHYON-105 Update debug string concat to use SLF4J parameterized feature
Seemed like weird Github diff since I don't see extra spaces in the editor.