Dash-bootstrap-templates

Fixed
- relaxed install versions

Changes
- updated the dbc.css to improve style when switching themes.

Boostrap V5 stylesheets.

Added
- added "QUARTZ", "MORPH", "VAPOR", "ZEPHYR" themes
- added 2 All-In-One components to switch themes.
- `ThemeSwitchAIO` toggles between two themes
- `ThemeChangerAIO` opens a Offcanvas component to select any of the 26 themes
- `template_from_url` helper function to get the figure template name for the selected theme
- added `dbc.css` which minimally styles `dash-core-components` and the `DataTable` with the selected Bootstrap theme
- added examples of the2 AIO components that switch themes.

Changes
- updated `_create_templates.py` to generate figure templates based on Boostrap V5 stylesheets

This is the initial release of `dash-bootstrap-templates` which includes a collection of 22 Plotly figure templates customized
for Bootstrap themes. This is based on `dash` V1.21.0 and `dash-bootstrap-components` V0.21.0 which uses
Boostrap V4 stylesheets.

Find sample usage in the `examples/` folder