Add a re-direct to the updated `fastsolv` Solubility Predictor

[JacksonBurns]

We have developed a new and improved solubility predictor which is available at fastsolv.mit.edu.

This predictor has significantly improved accuracy for organic solvents, but is not recommended for use on water. We should:

• just suggest users go to it, and provide a link on the page
• auto-magically redirect users, somehow accounting for the fact that it doesn't work on water

We could also consider a more technical solution than a simple re-direct, like integrating the predictor into the website directly.

Opening this as a reminder/TODO for myself, and I welcome comments on the best way to implement this.

[jonwzheng]

Will implement a basic version of this (maybe just a link) in #298.