class added to login form
class added to login form

it's a bit tricky to style the login form since we don't have a
class. This PR adds a class, no sure about the official name
conventions here but it makes styling much easier.

Former-commit-id: 0d296eecf9992268eadc82efe4a0d2a9dd70aa97
MrKarlDilkington/concrete5,mainio/concrete5,jaromirdalecky/concrete5,hissy/concrete5,deek87/concrete5,haeflimi/concrete5,biplobice/concrete5,MrKarlDilkington/concrete5,a3020/concrete5,biplobice/concrete5,concrete5/concrete5,jaromirdalecky/concrete5,acliss19xx/concrete5,hissy/concrete5,mainio/concrete5,mainio/concrete5,mlocati/concrete5,olsgreen/concrete5,rikzuiderlicht/concrete5,olsgreen/concrete5,mlocati/concrete5,concrete5/concrete5,acliss19xx/concrete5,mlocati/concrete5,MrKarlDilkington/concrete5,biplobice/concrete5,jaromirdalecky/concrete5,a3020/concrete5,jaromirdalecky/concrete5,rikzuiderlicht/concrete5,concrete5/concrete5,acliss19xx/concrete5,concrete5/concrete5,olsgreen/concrete5,hissy/concrete5,biplobice/concrete5,rikzuiderlicht/concrete5,triplei/concrete5-8,KorvinSzanto/concrete5,deek87/concrete5,haeflimi/concrete5,triplei/concrete5-8,KorvinSzanto/concrete5,deek87/concrete5,deek87/concrete5,haeflimi/concrete5,triplei/concrete5-8,hissy/concrete5,mlocati/concrete5,KorvinSzanto/concrete5,haeflimi/concrete5