PLD: remove is_deleted field and references to it, closes #111
raise ValueError only if there is a single result whose value is None
PLD: fix deleted_at test check
added libs module to installed apps to have its tests run
fixed todo descr. on count test
add ondadata.libs to travis tests
UK: using count(*) ensures null columns are counted
PLD: remove commented code
PLD: remove comment
Merge pull request #132 from onaio/empty_aggregation_fix

Fix logic used to determine invalid field requests
PLD: changes surveys to instances, closes #127
PLD: migration order
Merge pull request #133 from onaio/instances-name-127

Instances name 127
Merge branch 'master' into graphs

Conflicts:
	onadata/libs/data/tests/test_tools.py
table formatting
moved tests to within utils dir
consider start, end, today and datetime as time fields
Statistics helper to calculate stats from basic values
Statistics on charts