[popover] got rid of flickering when mdl-select drop-down do not have enough space available at the bottom
[popover] got rid of flickering when mdl-select drop-down do not have enough space available at the bottom

mseemann/angular2-mdl-ext,mseemann/angular2-mdl-ext,mseemann/angular2-mdl-ext,mseemann/angular2-mdl-ext