Update Hive icon and add Hive Web to the list of wallets

As you might know, our HTML5 wallet Hive Web has now been out for a while and has generally been well received (see this Coindesk article, for example: http://www.coindesk.com/hive-web-wallet-bitcoin-adoption-roadblocks/ ).

We would therefore like to extend our wallet listing to the web section. This pull request contains a description for Hive Web, a screenshot and also changes the Hive icon to the latest version.

Security-wise Hive Web is similar to Blockchain.info, however the user's BIP32 passphrase never leaves their computer, so isn't stored on our servers in any way.

I hope this can be merged. Let me know if you have any questions or would like to see changes made. Thanks!