0.6.2

Features
* in plots show x-axis label on hover, helpful when x-label on bottom is abridged (pld)
* option to flatten summary (pld)
  * API change: new "flat" parameter to /datasets/[ID]/summary
  * edge cases may not be covered, once we begin using this we can clean it up


* dates can now be passed in query params as "YYYY-MM-DD" or anything else dateutil.parser.parse can handle
  * this includes fetching data and plotting, e.g.
  * please file an issue if you find an endpoint that's missing this or see an exception raised, it's WIP
* more params for plot endpoint
  * height, width, and palette can all know be passed
* vega output from plot, pass vega=True for vega JSON output
  * note this only outputs the first column, if this will be used we can generalize it
* datasets with overlapping columns can be joined
  * the duplicate columns are renamed "original.x" for the left and "original.y" for the right 
* replace a dataset's content without changing the ID
  * API CHANGE: /dataset/[DATASET ID]/reset, takes the same params as create
  * /dataset/create can take a dataset_id param to operate equivalently to reset
* delete all rows matching a query
  * API CHANGE: /dataset/DATASET ID]/delete now takes an optional query JSON spec param

Fixes
* correctly encode nested queries (rgaudin)
* correctly show success message on add calculation (rgaudin)