Changes

Use unix timestamps in the SMS db

There's really no need to convert to/from human readable
dateformat (YYYY-MM-DD HH:MM:SS) everytime we access a record in
the SMS database.

sqlite3 has pseudo column types. In fact this means the column type
in the database schema is meaningless and anything will be accepted
and stored. See (Flexible Typing) [1]

It appears that more processing than might be expected
is happening internally on such things as date conversions, as
the database engine has to actually do verifications on the data.
(Is this INT really an INT etc...)

[1] https://www.sqlite.org/quirks.html

Change-Id: I599a57666da22adf806b01ff095c8672d523a737