…ties - MEED-7094 - Meeds-io/MIPs#144 (#3916)

This change will apply **application-background** class to the main body
of applications to make sure to apply layout specific CSS styles, such
as disabling default Vuetify White Background applied on v-card. At the
same time, for Top Toolbar applications, this will disable branding
styling to avoid having border radius and other styles applied on small
buttons added in Top bar as applications.

…o/MIPs#144 (#3922)

…3925)

 - Meeds-io/MIPs#144

…ED-7099 - Meeds-io/MIPs#144 (#3930)

#3931)

This change will introduce a new Field to allow adding a custom global
CSS. This feature can be enabled using a feature flag.

… (#3941)

This change will apply new font sizes:
- Title: 20px, regularColor, Bold
- Header: 18px, lowImportanceColor, Regular
- Body: 16px, regularColor, Regular
- Subtitle: 12px, lowImportanceColor, Regular

This change will apply new font sizes:
- Title: 20px, regularColor, Bold
- Header: 18px, lowImportanceColor, Regular
- Body: 16px, regularColor, Regular
- Subtitle: 12px, lowImportanceColor, Regular