Fix grey color on white background

Part of #105 

Initial thoughts on how to clean up our grey usage.  This isn't complete yet.   Please review and let me know if you have any concerns or ideas.

Concerns:
* 333 and 666 aren't that easy to distinguish.  See the hover state.
* Zero state title is pretty bold now.  We could make it the same color as the text if we wanted.

Outstanding Items:

* Loading icon
* Might try a function to "lighten" text.  Unclear to me how easy this will be to actually use though.
* Might try to have better names than weights, more in context

Table Headers
![2014-10-23_11-23-01](https://cloud.githubusercontent.com/assets/309711/4755901/337657b8-5ac9-11e4-8209-83c6fc3d0389.png)

Zero State (the header seems a little dark to me now)
![2014-10-23_11-24-11](https://cloud.githubusercontent.com/assets/309711/4755906/3da1e6b2-5ac9-11e4-8d78-3a1e1e330cf6.png)

Loading (text only)
![2014-10-23_11-24-53](https://cloud.githubusercontent.com/assets/309711/4755924/5bf27c4e-5ac9-11e4-8537-a09806dc9f17.png)

Subtext
![2014-10-23_11-24-23](https://cloud.githubusercontent.com/assets/309711/4755923/570beac6-5ac9-11e4-82b1-0871622eec94.png)

Progress subtext
![2014-10-23_11-26-15](https://cloud.githubusercontent.com/assets/309711/4755928/62ee6968-5ac9-11e4-972e-3f603f653799.png)