change data.preview .config to load data file or data uri with data.view settings specified in that config file

[RandomFractals]

trafficstars

currently .config data.preview shows that json config file properties grid which is not as useful.

also, this change will allow to live share remote data previews as defined in #16 and allow to edit raw data.view config json and see changes in the corresponding webview

[RandomFractals]

user SpaceX launches .config for testing :) https://github.com/RandomFractals/vscode-data-preview/blob/master/data/json/spacex-launches.config

Expected: data preview loads SpaceX data from this data uri: https://api.spacexdata.com/v3/launches and sets displayed columns, sort, etc.