[ZcF-general] ZecWallet March update

[adityapk]

Lots of improvements for ZecWallet this month

ZecWallet:
- Rename to ZecWallet, with a new logo!
- Launch the ZecWallet doc site (https://docs.zecwallet.co) (Gareth) and the usage videos (Dimitris)
 - Experimental headless mode with ZecWallet to allow nodes that can run in the background and connect to your phone
- Add rescan / reindex options in the UI for troubleshooting
- Automatic URI handling for the zcash: protocol in Win, Linux, Mac, Android
- Support for requesting money (and paying requests), Venmo style!
- Update zcashd to 2.0.4
- Remove Sprout receiving support

ZecWallet Android:
 - Allow replying to and composing messages on Android
 - Payment URIs support
 - Improve wormhole performance and connection longetivity

Others:
- A new repo (https://github.com/adityapk00/codesign) to allow easy codesigning using gpg for binary releases