Support for mutiple screen resolutions and breakpoints in grid

[przytu1]

Rough idea: treat grid_template as definition for one grid e.g. my_mobile_grid <- grid_template(x,y,z, breakpoint = 700px) my_desktop_grid <- grid_template(..., width/height = xyz)

and then render multiple templates in grid(list(my_mobile_grid, my_desktop_grid))