Ui: adapt popover styles to modal ones
Ui: adapt popover styles to modal ones

This commit add some rules to popover view, taken from modal view, such
as footer border-top style.

frankrousseau/cozy-calendar,nono/cozy-calendar,frankrousseau/cozy-calendar,cozy/cozy-calendar,Noctisae/cozy-series,jsilvestre/cozy-calendar,cozy/cozy-calendar,cozy-labs/calendar,poupotte/cozy-calendar,Noctisae/cozy-series,kelukelu/cozy-calendar,jsilvestre/cozy-calendar,kelukelu/cozy-calendar,lemelon/cozy-calendar,aenario/cozy-agenda,lemelon/cozy-calendar,aenario/cozy-agenda,nono/cozy-calendar,clochix/cozy-calendar,poupotte/cozy-calendar,cozy-labs/calendar