cubicweb-squareui #3597030 Clean the header HTML [validation pending]

Clean the header bar HTML (especially the authentification box)

prioritynormal
typeenhancement
done in0.3.0
load1.000
load left0.000
closed by<not specified>
patch[stateheader] make stateheader more user friendly (related to #3597030) [applied][header] make `main_header` more bootstrap compilant (related to #3597030) [applied]