Way to inject settings from backend into frontend

[fashxp]

define a way to get settings defined in symfony configuration, settings store, etc. into frontend application.

e.g. for

• page-size for trees
• colors for customizing
• etc.

[mattamon]

A simple route should be enough here to provide a fixed set of settings and maybe a event to push custom settings into it if necessary (e.g. for bundles)

Settings that are stored in the core, should be no problem atm.

Settings that are stored in the Admin classic ui like branding, need to be redefined where to store them. (studio-ui or studio-backend, or in the core?)