Implemented UDFs for timestamp functions.

FromUtc and ToUtc use thirdparty libraries which use inline asm which
isn't currently supported with JIT. The UDFs are included in this
commit, but the function symbols were not changed in
impala_functions.py

Change-Id: I0824a434d4a26a39abf29bc6e47d51b5ad7991d6
Reviewed-on: http://gerrit.ent.cloudera.com:8080/3390
Reviewed-by: Paden Tomasello <paden.tomasello@cloudera.com>
Tested-by: jenkins