Change how validators are appended.
Validate queries are UTC midnight

@gtrogers
@pbadenski
Validate timezone is valid

@pbadenski
@gtrogers
Merge remote-tracking branch 'origin/master' into Fix_timezone_issues

Conflicts:
	tests/read/test_validation.py
	tests/read/test_validation_of_queries_accessing_raw_data.py
Merge pull request #53 from alphagov/Fix_timezone_issues

Fix timezone issues