Rename "Single Wallet" to "Unified Wallet" (#185)

* Rename "Single Wallet" to "Unified Wallet"

I've seen the term unified wallet more recently, and it seems to be more descriptive. If others agree, let's change the LDK home page.

* Update docs/index.md

Co-authored-by: Elias Rohrer <dev@tnull.de>

Co-authored-by: Conor Okus <conor.okus@hotmail.co.uk>
Co-authored-by: Elias Rohrer <dev@tnull.de>

Author: 3 people

docs/index.md

@@ -44,7 +44,7 @@ Use a local full node, an SPV node, or your own Electrum server with API access
 </div>
 
 <div class="feature">
-<h3>Single Wallet</h3>
+<h3>Unified Wallet</h3>
 
 No need to create separate Bitcoin & Lightning wallets, forcing users to backup an additional recovery phrase. Instead, we let you define your own wallet and create one unified experience.