Extend widgetpreview to contain preview for more components

[saemideluxe]

The widgets preview is very useful for a) quickly checking if widgets are rendered correctly and b) to give new developers an idea what form components we have available.

This should be extended to most other components as well. The widgetpreview view should be changed to be named "componentpreview" and contain five tabs. Each tab contains examples of different components. I suggest we use one tile (not expandable) per component class. One tile can contain multiple examples of the same component with different options. And each tile should have a two-column layout: In the first column we show the component examples and in the second we display the docstring of the components init method. That way we can also easily see which components are still missing good docstrings.

Here is the list of tabs and which modules should go into which tab:

1. Layout components
   • grid.py
   • tabs.py
   • modal.py
   • tile.py
2. Informational components
   • icon.py
   • tag.py
   • loading.py
   • progress_indicator.py
   • tooltip.py
   • notification.py
3. Interactive components
   • button.py
   • content_switcher.py
   • toggle.py
   • overflow_menu.py
   • pagination.py
   • searchbar.py
4. Datatable
   • datatable.py
5. Form components
   • content of current widgetspreview

[dward2nd]

Because this one is a bit long and detailed, it is best to keep tracking the progress so we can all see how it's been going.

1. Layout components

• [x] grid.py
• [x] tabs.py
• [x] modal.py
• [x] tile.py

2. Informational components

• [x] icon.py
• [x] tag.py
• [x] loading.py
• [x] progress_indicator.py
• [x] tooltip.py
• [x] notification.py

3. Interactive components

• [x] button.py
• [x] content_switcher.py
• [x] toggle.py
• [x] overflow_menu.py
• [x] pagination.py
• [x] searchbar.py

4. Datatable

• [x] datatable.py

5. Form components

• [x] content of current widgetpreview