Update guide with new features

[avive]

• Create page with description of all the contacts features. Should cover the following use cases:

1. Create a contact from an account that sent you coins.
2. Create a contact via the contacts screen.
3. Send coins to one of your contacts. Click on contact in the contacts screen, set amount and send...

• Update doing more with your wallet section to describe set rewards account feature.

• Create new page with information about the sign text feature.

All pages should have screen shots showing a synced node on the testnet.

[avive]

@yaelmhoffman - are we done?