Specify a start year in the consultations date_select

This prevents not being able to select a date when non is saved and the
year is set to 0001

https://www.pivotaltracker.com/story/show/47806169
Use validates_timeliness to check for date/time validation

Need to add to all the other models which have date/times
Setting a start year enables users to fix the 0001 year issue

Need to review all of these and agree with a defualt at the moment they
are a bit allover the place - using 2000 for now.
Move validates_datetime for first_published_at to edition
use 2000 as the default start year to allow backdating
validate from 1900 but set the date in forms to 1997