Rm auto width and height of button component metamodel

Regular buttons should use new css styling to set
width and height to standard sizes.

Authors can still hard-code width and height.

[#45690029]
Make nicer, scalable buttons, matching Upstatement's

Button font, dimensions and curvature are all set with
ems, allowing smooth scaling.

Also fix sass syntax for pulldown gradients

[#45690029]