Render headings, format columns, create data table, correct padding

- `_hasHeadings()` function added to check if a column has a label
- `_renderHeadings()` function complete, applies the `heading_font-style` class and sets the label on each customized column
- `_formatColumns()` function progress, calculates column widths and applies alignment
- `_createDataTable()` function complete
- corrected implementation of padding
- fixed e2e test