[IconButton] Is not theme-able and the default is off spec

[oisinlavery]

Problem description

IconButton is not fully theme-able.

https://github.com/callemall/material-ui/blob/master/src/IconButton/IconButton.js#L19

The padding, width and height are hardcoded to baseTheme.spacing.iconSize * 2
Assuming a size 24px icon this makes IconButton 48x48 by default.

This is off Google Material Design spec, IconButtons should have a 24px icon with 8px padding, giving an IconButton size of 40x40.

Angular Material and Polymer are correctly set to 40x40. In general Polymer is generally closest to being on spec.

Steps to reproduce

Versions

• Material-UI: 0.15.4
• React: 15.3.0
• Browser: n/a

[oisinlavery]

@oliviertassinari can this be labelled as a Material Design spec issue?