Allow custom tables that don't use jsonb

[yasserf]

Link to discussion somewhere in here https://github.com/deepstreamIO/deepstream.io-storage-postgres/pull/32

Idea is instead of doing this (in master currently):

id	version	val
mercedes	4	{ "color": "black" }
vw	20	{ "color": "red" }

we can do this:

id	version	color
mercedes	4	black
vw	20	red