adding todo table and add_todo stored_proc

[KurtStam]

and removing the demo_add function

@zregvart so we can update scenario 2 to use this

to test:

rsh syndesis-db-1-xxxxxx
sh-4.2$ psql -U sampledb -d sampledb
sampledb=> select add_todo('brand new task for testing');
sampledb=> select * from todo;
 id |            task            | completed 
----+----------------------------+-----------
  1 | kurt                       |         0
  2 | brand new task for testing |         0

[chirino]

LGTM

[pure-bot[bot]]

Pull request approved by @chirino - applying approved label