added default line height to accomodate multiple lines

Adds default line height to form buttons to accommodate for multiple lines.  Padding was tweaked to maintain vertical spacing. 

Resolves [1540](https://github.com/DoSomething/dosomething/issues/1540)
Because of the added line height.  Right now, on mobile, when the button reads 'Update Submission' it wraps to two lines and the default line height is pretty loose.