Add Date Variable in to Table

1. add a date attribute to the data table
2. show all data in descending order of date
Merge branch 'master' of https://github.com/ddp-medical/Path2health

Conflicts:
	app/models/datum.rb
	db/schema.rb

	modified:   app/models/datum.rb
	new file:   db/development.sqlite3
	modified:   db/schema.rb