Dataset interpolation #53

implement interpolation for numeric and geographic data
add is as editor action to apply directly to a datasets' data
enforce upper limit of visualization complexity
- making sure visualization rendering in clients isn't too computationally intensive
  * includes client-side performance
  * reduces resulting filesize
  * decreases ecological imact
- automatically interpolate visualized data
  - if it exceeds some configurable number of visualized points
    - either visualized numerical observations or
    - sum number of points in in visualized geodata columns)
- add interpolation data into visualizations, so readers are aware
  a visualization is not "lossless"