Now with added ceres
Adds support for constantLine function

* Also changes (temporary) fixed interval for sin & constantLine from
10s to 60s to match current ceres granularity
Adds support for 'offset' function.
* Scale & Offset now leave nulls as nulls after they've scaled/offset'ed
Adds initial support for output renderers (CSV, RAW,JSON)
Updated gridster to v0.2.1
Initial rough stab at chartled export.