Updates for version 3.0

Version 3.0 introduces breaking changes:

Removed viewport component, this extra layer was redundant;
Changed classes to complex names in order to support bootstrap and other libraries:
- row -> rgRow;
- col -> rgCol;
- data-cell -> rgCell;
- data-header-cell -> rgHeaderCell;
All methods migrated to lowercase in order to support the modern approach of event naming. It means events name migration: afterEdit -> afteredit for all events. Check api for details;
Added pure esm modules support in order to use the grid in all modern frontend tooling like vitejs, parcel etc, now you can import custom-elements without lazy loading, just keep in mind you are responsible for polifills.

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