Multiple bugs / feature suggestions around viz

[dustmop]

• No way to view the source of the viz using the frontend
• In viz editor, erasing all text goes back to the "Add Viz Script" button, making it tricky to erase then paste source from another file
• Would be nice to be able to render viz without saving, in order to develop using the frontend editor (like codepen)
• From dataset's landing page, clicking Edit, then adding viz, then clicking Save gives an error because the Dataset Name is blank (should be filled in with the current name instead)
• Suggestion: Dataset Name has an uneditable "me/" prefix before the input field