<IconButton> should support 'size'

[dylankenneally]

Issue:

• Using an <IconButton>, for example in an <ActionBarGroup>, it would be good to be able to add the size attribute in the same way we can when using an <Icon> object.

Example:

{/* React.JS based, these two lines have the same output */}
<ActionBar>
  <ActionBarGroup>
    <IconButton icon="grid" title="grid" type="flat"/>
    <IconButton icon="grid" title="grid" type="flat" size="16" />
  </ActionBarGroup>
</ActionBar>

{/* These two lines have the desired output of the above */}
<Icon nameOrSVG="grid" />
<Icon nameOrSVG="grid" size="16" />

Expected result:

• Support small sized icons

[rminderhoud]

Adding my support for this feature