Add Save as CSV or JSON data UI options

[RandomFractals]

Use Tabulator Download API for this feature implementation:

http://tabulator.info/docs/5.0/download

and Data Preview Save UI setup: https://github.com/RandomFractals/vscode-data-preview/blob/master/web/data.view.html#L26

 <select id="save-file-type-selector" 
          title="Save Data View .config or Data" 
          onChange="saveData()">
          <option value="">📥&nbsp;Save</option>
          <option value=".config">⚙️ &nbsp;config</option>
          <option value=".arrow">⋙ arrow</option>
          <option value=".csv">,,, csv</option>
          <option value=".json">{} &nbsp;json</option>
...

with the saveData JS: https://github.com/RandomFractals/vscode-data-preview/blob/master/web/scripts/data.view.js#L402

function saveData() {
	const dataFileType = saveFileTypeSelector.value;
	switch (dataFileType) {
...

and saveData TS from Data Preview extension: https://github.com/RandomFractals/vscode-data-preview/blob/master/src/data.preview.ts#L712

[RandomFractals]

added Save as CSV or JSON data UI options: