Share methods to set the theme color classes

[devversion]

We need to find a way to share the methods, which apply the theme color classes on the components.

Right now we are repeating the same methods for each component.

• Also we should have a type for the color values like primary | accent | warn

[david-kerwick]

Would it be possible to expose this globally so we could use it in any component?
I'm following https://github.com/angular/material2/blob/master/guides/theming-your-components.md at the moment, but it means I need to stick the imports on top of all the components. Having access to a global primary | accent | warn would be great

[devversion]

Would be weird to have a shared code for the theme classes- because we would need our renderer from the DI in that utility. Let's revisit this later.