Derivative and integral steps (#2)

**TODOs**

- [ ] Replace all dummies immediately when printing
- [ ] Refactor `MultiResultCard` so that results can be retrieved incrementally (rather than having to wait for all computations to finish)
- [x] Hide "integral steps" card unless steps exist
- [x] Link to specific cards 
- [x] Replace `+ Symbol('constant')` with just adding `+ \mathrm{constant}` to the printed output.
- [x] Add version and SymPy git hash to about page
- [x] Add separate error for timeouts
- [x] Fix bug in JavaScript (http://sympy-gamma-li.appspot.com/input/?i=E)

Changes:

- Integral steps
- Derivative steps
- Formatting & style changes

Integral & derivative steps are the same as before. There are improvements that could be made but they work.

Formatting & Style:

- Make example column headers larger (easier to hit on mobile, fits motif of result page)
- When not logged in, make the example column wider

![Screenshot from 2013-04-09 13:41:56](https://f.cloud.github.com/assets/327919/359122/ef70db2a-a155-11e2-90ec-223ae2b09ff9.png)

![Screenshot from 2013-04-09 13:42:31](https://f.cloud.github.com/assets/327919/359125/02b40af4-a156-11e2-90c3-4ffb57603753.png)

- Add live preview of input

![Screenshot from 2013-04-09 13:43:41](https://f.cloud.github.com/assets/327919/359137/2f87c2a0-a156-11e2-86b5-f26f90690ea5.png)
![Screenshot_2013-04-09-13-44-23](https://f.cloud.github.com/assets/327919/359145/59ed37d2-a156-11e2-8a33-8e828e5bd25a.png)
![Screenshot from 2013-04-09 13:46:27](https://f.cloud.github.com/assets/327919/359153/9540bed0-a156-11e2-8229-71174bfe3693.png)

- Add "See Steps" to integral card

![Screenshot from 2013-04-09 13:48:05](https://f.cloud.github.com/assets/327919/359166/dfeb6138-a156-11e2-8fff-4a60f6259b10.png)

- Improve formatting of `limit`

![Screenshot from 2013-04-09 13:48:22](https://f.cloud.github.com/assets/327919/359167/e55ea738-a156-11e2-83ea-4097dd11d4aa.png)