Added two additional date formats to check for, moved conversion to its
own function.  Also added a unit test.
Is there a prettier way to do this than these nested try/except blocks?
Cleaned up structure for timestamp converter

Also added test to verify that unsupported formats get logged.
Merge branch 'master' of https://github.com/dimagi/commcare-hq
Merge pull request #754 from esoergel/master

Added two additional date formats to check for