- Changed variants of buttons to unify the look and feel
- Added support for themes specified in Theme.css
- Added a new dependency "react-select" for selecting themes.

Select component now shows the correct color.

Removed bootstrap-dark from dependencies.
The current theme is now synchronized with the react select component.

This PR comes with the following fixes:

- Pastel theme should now be darker
- Added a preference tab
- Font size of the selector has been reduced
- Fixed css
- Moved AppContext under src/contexts
- Renamed themes to provide backwards compatibility

- Added a darker background for the theme "dark"
- Added stripes back to the tables
- Moved css files in src/css
- Removed the Themeselector as it now implemented in PreferencesView

The editor should now have the correct theme settings.

Moved index.css to css folder.

Tables should not be readable in dark mode