[ADD] report,base: custom report layouts

External layout for reports can be customized. 4 Layout are currently
proposed, selectable from General Settings.
An onboarding popup is shown to select the layout to used if none has
been shown nor a company logo chosen.

Joint works by Fabien Pinckaers, Antony Lesuisse and Christophe Simonis.
Design by Csaba Fazekas.