Charts now look much sharper

To get everything looks sharper, move the main container 0.5 pixels in each direction. It's a known issue on D3 (check http://mbostock.github.io/d3/tutorial/bar-2.html). Half-pixel offsets disable anti-aliasing.

Additionally, some values gets rounded and some elements get sharpened by CSS.

Know bugs: 
- grid-lines sometimes have an offset of 1px
- does not work after windows.resize

**Comparison:**

Before:

![unsharp](https://cloud.githubusercontent.com/assets/1242960/2862521/7d025944-d1f4-11e3-8724-71f80264b121.jpg)

After:

![sharp](https://cloud.githubusercontent.com/assets/1242960/2862522/818898ca-d1f4-11e3-8569-003b1bde8fdb.jpg)