Change margin to padding to allow custom css

[ralberth]

Bringing over a comment from a closed issue here so it can be tracked separately.

Original comment:

It might be a good idea to change the margin style in MMM-ScriptScheduler.js to padding because else margin can not be set in the custom.css. That shouldn't have any negative effect but would make it easier to position the icon/image individually. For example did I center the icon/image in custom.css with margin: 0 auto;