Add post rating slider

[generic-github-user]

Buttons should be placed at the beginning, end (and possibly the middle) of the sliders so that people can rate 0 or 100 easily.

[generic-github-user]

In progress . . . looks like I may have messed something up . . .

[generic-github-user]

After playing with a slider for some time, I don't think that it'll produce the best user experience. A series of buttons may be a better option.

[generic-github-user]

I am now using colored buttons instead of a slider: #31

[generic-github-user]

I really like the idea of a slider, but it just doesn't "feel right" - a button represents a more resolute action, has a more tactile feel, and is more interesting and satisfying to interact with.