Set Electrum as the recommended desktop wallet

As suggested by @mikehearn, it seems more reasonable to remove the "Third party" disclaimer. Electrum is now connecting to a random server from a list of 22 servers at each startup.

Additionally, I'd like to suggest we replace MultiBit by Electrum as the "default" recommended wallet for Desktops for the following reasons:

Deterministic wallets ( No address reuse ).
Offers a good backup plan to the user at first start.
Easier to install ( No Java, MultiBit Linux installer has a few glitches )

Many nice features from MultiBit are also supported by Electrum, like localization and loading/saving wallets from/to files. Maybe MultiBit could be set as the default wallet again once MultiBit HD is released. Meanwhile, promoting a different wallet would promote a little more diversity.