Add missng style to default theme

[stuartmanderson]

The default theme default.css script appears to be missing a style:

a.button, input[type="submit"], input[type="button"], ul.button-nav li a, div.generic-button a {
...
}

The above needs the style input[type="reset"] adding so that "Reset" buttons also pick up the button styling.

[johnjamesjacoby]

(In [3047]) Addresses #1566. Add styling to reset buttons. Mostly for child themes and custom components that use these.