Add a lower severity disclaimer for wallets in-between software wallets and web wallets.

This disclaimer is meant to allow visitors to be better informed of the difference between fully open-source and decentralized wallets and those who partially depends on centralized and opaque services.

Applies to hybrid wallets (blockchain.info)
Applies to clients that are loading the block-chain using a centralized server (Electrum, Mycelium)

Concerning blockchain.info, if anyone still feel it should have the big red warning, I'm OK with that too. However my personal opinion is that this disclaimer is better suited given that it explicitely recommends using strong passwords and backups, and since we are linking and recommending the Android app and browser extension.

Screenshot:
![capture du 2013-08-15 22 45 51](https://f.cloud.github.com/assets/3578089/973292/2e281f56-0621-11e3-9a02-d282bdf96aa3.png)