Add new mapping options "table+json" and "table+jsonp"

[amotl]

Dear Daniel and all contributors,

first things first: Thanks for conceiving and maintaining this great plugin, we are using it extensively for displaying geospatial information with the Hiveeyes Project.

In one of our data planes, we are feeding data from the luftdaten.info project into an InfluxDB database using luftdatenpumpe.

As the data from InfluxDB is designated by "FORMAT AS Table" into the Worldmap Panel, we couldn't find a way to acquire the Location Name from a JSON/JSONP data source as it is possible with the "FORMAT AS Time series" variant already.

This PR accounts for that. When choosing to load location data using the new mapping options "table+json" or "table+jsonp", it is possible to load location information from JSON. The value of the data field designated by the "Location Name Field" will be used as a key for looking up the appropriate record in the JSON dataset. If the lookup fails, the specific code path is backward compatible and should produce the same results as before by using the value of the "Location Name Field" itself.

By applying that to our installation, we have been able to display a long location name acquired from ldi-stations.json on the map overlay of LDI stations map without having to store the name inside the InfluxDB measurement table itself. We don't even want to keep a short name there, the lookup is solely done by using a single location identifier, the numeric station_id:

With kind regards,
Andreas.

P.S.: This might also help along with #176.

[CLAassistant]

All committers have signed the CLA.

[amotl]

This has been superseded by #197.