Better handle errors with missing data from API
Prevent unit from being added when none found
Display seconds in dates and use 24h format
Refactor plot series handling
Fix issue with DST in `DurationToRange' tests
Merge branch 'oper-series'

Conflicts:
	cmd/facette/facette_test.go
	cmd/facette/js/graph.js
	pkg/server/api_library_graph.go