(Settings) Configure URL options

- HTML structure/markup for URL options (Cells, Range, Worksheets, Number of Header Rows)
- Locale translations for new HTML markup/structure in english JSON
- Added new private vars for storing URL options
- Caching new elements
- Removing unnecessary console logs
- Optimized _getSheets function
- Followed through on logic for successful retrieval of sheets involving
- New private function _onSheetsLoaded for adding the option elements to the worksheets select element
- New private function _onShowDataURLOptions for configuring URL and showing URL options